In practice, however, unless the President were unconscious, the public could see the use of the amendment as a constitutional coup. Measuring deterioration over time would be difficult in Trump’s case, given that his “judgment” and “ability to communicate clearly” were, in the view of many Americans, impaired before he took office. For those reasons, Robert Gilbert, the Presidential-health specialist, told me, “If the statements get too strange, then the Vice-President might be able to do something. But if the President is just being himself—talking in the same way that he talked during the campaign—then the Vice-President and the Cabinet would find it very difficult.”

The power of impeachment is a more promising tool for curtailing a defective Presidency. The Framers considered the ability to eject an executive so critical that they enshrined it in the Constitution even before they had agreed on the details of the office itself. On June 2, 1787, while the delegates to the Constitutional Convention, in Philadelphia, were still arguing whether the Presidency should consist of a committee or a single person, they adopted, without debate, the right to impeach for “malpractice or neglect of duty.” They gave the House of Representatives the power to impeach a President for “treason, bribery or other high Crimes and Misdemeanors” by a simple majority vote, and they gave the Senate the power to convict or dismiss the charges, setting a high bar for conviction, with a two-thirds majority.

But what would “high Crimes and Misdemeanors” mean in practice? In 1970, during an unsuccessful effort to impeach the Supreme Court Justice William O. Douglas, Representative Gerald Ford argued that an impeachable offense was “whatever a majority of the House of Representatives considers it to be at a given moment in history.” That was an overstatement—the President was never intended to serve at the pleasure of Congress—but it contained an essential truth: impeachment is possible even without a specific violation of the U.S. Criminal Code. When Alexander Hamilton wrote of “high Crimes,” he was referring to the violation of “public trust,” by abusing power, breaching ethics, or undermining the Constitution.

The first test came with the impeachment of Andrew Johnson, in 1868. Johnson, who became President after Lincoln’s assassination, was a combative Tennessean, sympathetic to the Southern states, and was uncomfortable in Washington, which he disparaged as “twelve square miles bordered by reality.” He mocked the legislative branch as “a body called, or which assumes to be, the Congress,” and vetoed the Civil Rights Bill of 1866, which was intended to confer citizenship on freed slaves. Congress was incensed; Senator Carl Schurz, of Missouri, compared Johnson to “a wounded and anger-crazed boar.” Eventually, the President engineered a showdown with Congress, by deliberately breaking a law against firing a Cabinet secretary without Senate consent. As a result, the House moved to impeach him, accusing him of “denying” the work of another branch of government and “preventing the execution” of laws passed by Congress. Johnson was acquitted in the Senate by one vote.

David O. Stewart, the author of “Impeached,” a history of the case, told me that it established a crucial point: impeachment is not a judicial proceeding but a tool of political accountability. “Because of the unique powers of the executive, we are depending on a single person to be wise and sane,” Stewart said. “If, in fact, there are enough people who no longer think those are both true, impeachment is designed to deal with that.” For this reason, actual evidence of misconduct may not be the most important criterion in determining which Presidents get impeached. “The most important thing is political popularity,” Michael J. Gerhardt, a professor of constitutional law at the University of North Carolina, told me. “A popular President is unlikely to be threatened with impeachment. Second is your relationship with your party—how strongly are they connected to you? Third is your relationship with Congress, and fourth is the nature of whatever the misconduct may be.”

By far the most valuable lessons about impeachment come from Richard Nixon. In 1974, Nixon resigned shortly before he could be impeached, but his misjudgments—political, psychological, and legal—have illuminated the risks to Presidents ever since. In 1972, Nixon’s White House oversaw the bugging of the Democratic National Committee offices at the Watergate complex and the ensuing coverup. That was illegal and unethical, but it did not guarantee Nixon’s downfall, which came about because of two critical mistakes.

First, when the scandal emerged, the President underestimated the threat. “There were any number of steps that could have made it go away,” Evan Thomas, the author of “Being Nixon,” told me. “They could have cleaned house and fired people.” But Nixon assumed that his supporters would never believe the accusations. “He was ahead by thirty-four points in the polls in August, 1972,” Thomas went on. “He could have taken his clothes off and run around the White House front yard and he was going to win reëlection.”

As the scandal ground on, Nixon made his second mistake: he flouted the authority of a coequal branch of government. In October, 1973, Nixon refused to obey a federal appellate-court ruling that ordered him to turn over tapes of conversations in the Oval Office, and he forced out the investigation’s special prosecutor, Archibald Cox. For nine months, Nixon continued to resist—in effect threatening the basic constitutional system—until, in July, 1974, the Supreme Court ruled that he had to comply. By then, the damage was done, and the House Judiciary Committee launched impeachment hearings. By thwarting other branches, Nixon weakened his support in Congress and convinced the country that he had something to hide. Until that point, much of the public had not focussed on the slow, complex investigation, but interviews at the time show that Nixon’s stonewalling made people pay attention, and he never recovered. “Well, everything has added up to his incompetence over the last few months, and I don’t think the American people should stand for it any longer,” a woman interviewed in New York by the Associated Press said. “In fact, I just signed an impeach petition.”

By August, many of his top aides had been indicted, and polls showed that fifty-seven per cent of the public believed that Nixon should be removed from office. On August 6th, after a tape recording surfaced which captured him orchestrating the coverup, he was abandoned by Republicans who had previously derided the Watergate scandal as a witch hunt. Senator Barry Goldwater, of Arizona, told colleagues, “Nixon should get his ass out of the White House—today!” On August 9th, Nixon sent a letter to Secretary of State Henry Kissinger: “Dear Mr. Secretary, I hereby resign the Office of President of the United States. Sincerely, Richard Nixon.”

A quarter century later, the Bill Clinton impeachment yielded two related lessons—one about the path into crisis, and one about the path out of it. The first lesson was that investigations beget investigations. In January, 1994, when a special prosecutor started looking into Bill and Hillary Clinton’s investments in Whitewater, a failed Arkansas real-estate deal, there was no way to anticipate that it would conclude, nearly five years later, with Clinton’s impeachment for trying to cover up an affair with Monica Lewinsky, a twenty-two-year-old White House intern. Many raged against the conduct of that inquiry, accusing Kenneth Starr, the independent counsel, of abusing his powers, but the outcome demonstrated that a White House under investigation is in danger of spiralling into crisis.

The second lesson of the Clinton impeachment comes from the strategy adopted by his legal team. Learning from Nixon’s fate, the lawyers realized that congressional Democrats would abandon Clinton if they concluded that he had lost the trust of the public. Gregory Craig, one of the lawyers who directed Clinton’s defense, told me recently, “The fundamental point is that it’s a political process.” He and his team spent less energy on disputing the details of evidence than on maintaining support from fellow-Democrats and from the public. They painted Clinton as the victim of a partisan quest to exploit an offense—covering up an affair—that was not on the scale of abuse that the Framers had in mind. “To be honest, we pursued a strategy that embraced polarization,” Craig recalled. “I gave a statement to the press that said this is the most unfair process since the Inquisition in Spain. Some arcane historical reference came out of my mouth. I said, ‘It’s like they’ve tied up President Clinton, put him in a closet in the middle of the night and turned off the lights, and they’re whipping him.’ ”

The strategy succeeded. By the time the House impeached Clinton, on December 19, 1998, his approval rating had risen to more than seventy per cent—his highest level ever. “It’s a vindictive party that just went out to get him,” a man at an American Legion post in San Diego told a reporter, in December, just before the House voted to impeach. When the case reached the Senate, Clinton’s lawyers capitalized on his popularity and presented his misdeeds in the broader context of his Presidency. In closing arguments, Charles Ruff, the White House counsel, asked, “Would it put at risk the liberties of the people to retain the President in office?” The Senate acquitted Clinton on all charges.

Were Trump to face impeachment, his lawyers would likely try to present him as a victim of a partisan feud, but his unpopularity would be a liability; Republicans in Congress would have little reason to defend him. Nonetheless, the Clinton impeachment may contain an even larger warning for Democrats in pursuit of Trump. “It’s pretty important to be seen in sorrow rather than anger,” Stewart, the historian of impeachment, said. “Don’t emerge red in tooth and claw. That’s not merely tactical—it’s good for the country, because you should only pursue impeachment if you really have to.”

Not long ago, the topic of impeaching Trump occupied a spot on the fringe of Democratic priorities somewhere around the California secessionist movement. “If you’d have asked me around Election Day, I would have said it’s not realistic,” Robert B. Reich, Clinton’s Secretary of Labor, told me in April. “But I’m frankly amazed at the degree of activism among Democrats and the degree of resolution. I’ve not seen anything like this since the anti-Vietnam movement. ” In April, Reich, who is now a professor of public policy at the University of California, Berkeley, released an animated short, mapping out the path to impeachment, and it became an unlikely viral hit, attracting 3.5 million views on YouTube in the first twenty-four hours.

Because the Republican leadership in the House of Representatives will almost certainly not initiate the ouster of a Republican President, the first step in any realistic path to impeachment is for Democrats to gain control of the House. The next opportunity is the 2018 midterm elections. Republicans have been relatively confident, in part because their redistricting in 2010 tilted the congressional map in their favor. But Douglas Holtz-Eakin, a Republican economist and the president of the right-leaning American Action Forum, believes that the chances of control shifting to the Democrats is greater than many people in either party realize. “After a party takes the House, the Senate, and the White House, they typically lose thirty-five seats in the House in the next midterm,” he told me. “Republicans now hold the House by twenty-three seats, so, as a going proposition, they’re in trouble. They need to do really, really well.”

Unfortunately for the congressional G.O.P., unpopular Presidents sow midterm fiascos. Since 1946, whenever a President has had an approval rating above fifty per cent, his party has lost an average of fourteen seats in the midterms, according to Gallup; whenever the rating has been below fifty per cent, the average loss soars to thirty-six seats. Steve Schmidt, the Republican consultant, is concerned that, in 2018, the Party faces a convergence of vulnerabilities akin to those which pertained during the 2006 midterms, whose outcome George W. Bush characterized as “a thumping.” Schmidt told me, “The last time Republicans lost control of the House of Representatives, it was on a mix of competency—Iraq and Katrina—and corruption in government, with the Tom DeLay Congress.” The Trump Administration has a comparable “basic competency issue,” he said. “The constant lying, the lack of credible statements from the White House, from the President on down to the spokesperson, the amateurishness of the threats to the members of Congress, the ultimatums, the talk of ‘enemy lists’ and retribution.”

Tom Davis, who twice led Republican congressional-election efforts during fourteen years as a representative from Virginia, believes that his former colleagues are overly complacent. “These guys need a wake-up call. They’re just living in la-la land,” he said. He pointed out that regardless of the final outcome of an attempt to impeach—the two-thirds majority in the Senate remains a high bar to clear—Democratic control of the House would immediately make Trump more vulnerable to investigations. “If the gavels change hands, it’s a different world. No. 1, all of his public records, they will go through those with a fine-tooth comb—income taxes, business dealings. At that point, it’s not just talk—they subpoena it. It gets ugly real fast. He has so far had a pass on all this business stuff, and I don’t know what’s there, but I’ve got to imagine that it’s not pretty in this environment.”

If Democrats retake the House, the Judiciary Committee could establish a subcommittee to investigate potential abuses and identify specific grounds for impeachment. The various investigations of Trump already in process will come into play. In addition to allegations of business conflicts and potential Russian collusion, Trump is facing dozens of civil proceedings. In a case in federal court, he is accused of urging violence at a campaign rally in Louisville, Kentucky, in March, 2016, where he yelled, referring to a protester, “Get ’em out of here.” In a New York state court, he is facing a suit brought by Summer Zervos, a former contestant on “The Apprentice,” who alleges that he sexually assaulted her in 2007. The constitutional question of whether a President could be impeached for offenses committed before he took office is unsettled, but, as Clinton’s case showed, civil proceedings contain risks whenever a President testifies under oath.

Many scholars believe that the most plausible bases for a Trump impeachment are corruption and abuse of power. Noah Feldman, a Harvard Law School professor who specializes in constitutional studies, argues that, even without evidence of an indictable crime, the Administration’s pattern of seemingly trivial uses of public office for private gain “can add up to an impeachable offense.” Last week, after the State Department took down an official Web page that showcased Trump’s private, for-profit club, Mar-a-Lago, Feldman told me, “A systematic pattern shown through data points would count as grounds for impeachment.” He said that economic analysis of the former Italian Prime Minister Silvio Berlusconi’s self-enrichment proves the concept. “Berlusconi is said to have gained at most one per cent per business transaction from his Presidency, but that added up to more than a billion euros,” Feldman said.

Allan J. Lichtman is an American University historian who has correctly forecast every Presidential election since 1984 (including Trump’s victory). In April, he published “The Case for Impeachment,” in which he predicted that Trump will not serve a full term, because of a “Nixonian” pattern of trespassing beyond constitutional boundaries. He cited an incident in late January, during the legal battle over Trump’s first executive order on immigration. James L. Robart, the U.S. district judge who blocked the order, rejected the White House’s claim that the court could not review the President’s decision, ruling that the executive must “comport with our country’s laws, and more importantly, our Constitution.” Trump’s response was a further violation of democratic norms: he disparaged Robart as a “so-called judge” and said that he should be held responsible for future terrorist acts on Americans. “If something happens blame him and court system. People pouring in. Bad!” Trump tweeted.

Senator Richard Blumenthal, a Connecticut Democrat who is on the Judiciary Committee, believes that the Administration’s actions denigrating or denying the power of equal branches of government portend a “constitutional crisis” akin to Nixon’s refusal to accept the appellate-court judgment regarding the White House tapes. Last week, lawmakers from both parties announced that White House officials had refused a request from an oversight committee to turn over internal documents related to the hiring and resignation of Michael Flynn. In a letter to the House oversight committee, Marc T. Short, the White House director of legislative affairs, said that the Administration is withholding documents because they “are likely to contain classified, sensitive and/or confidential information.” Blumenthal told me, “I foresee a point that there will be subpoenas or some kind of compulsory disclosure issued against the President or the Administration by one of the investigative bodies—the F.B.I. or the Intelligence Committee or an independent commission, if there is one—and, at that point, there may be the sort of confrontation that we haven’t really seen in the same way since United States versus Nixon.”

Trump campaigned as a dealmaker who could woo disparate Republicans. Though there was no natural Trumpist wing of the Party, he was expected to ally with the three dozen conservative members of the Freedom Caucus, who tended to admire his anti-establishment populism. But the relationship descended into acrimony almost immediately. After the caucus objected to part of Trump’s effort to repeal and replace Obamacare, leading to the collapse of the bill, Trump publicly threatened to target its members in next year’s elections. “The Freedom Caucus will hurt the entire Republican agenda if they don’t get on the team, & fast,” he tweeted. “We must fight them, & Dems, in 2018!”

He went after individual members as well. At one point, he threatened to support a primary challenger against Mark Sanford, the South Carolina congressman. I asked Sanford if he regarded the threat as a bargaining tactic. “I think it was genuine,” he said. “It certainly wasn’t said in a way that suggested a bluff and then a wink and a nod.” Sanford said, of the level of support for Trump among Republicans in Congress, “In general, the mood of the conference is that we’re in the same boat together.” But he added a caveat: “This has to fundamentally be a game of addition, not just subtraction. I’m not sure the Administration has fully grasped that concept yet. You’re probably not adding to the list of permanent allies and friends.” He went on, “I think that there’s a degree of immunity that has come with the way that he has broken all of the past molds. But I would also argue that there’s a half-life to that.”

Trump is not faring much better with moderate Republicans. At a meeting in March, Charlie Dent, a seven-term centrist congressman from Pennsylvania, expressed misgivings about the health-care plan, and Trump lashed out. “He said something to the effect that I was destroying the Republican Party,” Dent told me. “And that the tax reform is going to fail because of me, and I’d be blamed for it.” In targeting Dent, Trump found an unlikely antagonist. Dent co-chairs an alliance of fifty-four moderate Republicans so resolutely undogmatic that they call themselves simply “the Tuesday Group.” Dent said that he remains ready to back Trump “when the President is on the right track,” but he left no doubt that he would break when his conscience requires it. “We have to serve as a check. I mean, that’s kind of our one power. We should accept that.”

William Kristol, the editor-at-large of The Weekly Standard, one of the most prominent conservative critics of Trump, told me that the Administration’s failure to get any bills passed was stirring frustration. “Most Republicans, I would say, wanted him to succeed and were bending over backwards to give him a chance,” Kristol said. “I think there was pretty widespread disappointment. You kind of knew what you were getting in terms of some of the wackiness and also some of the actual issues that people might not agree with him on—trade, immigration—but I think that just the level of chaos, the lack of discipline, was beginning to freak members of Congress out a little bit.”

Trump has been meeting with congressional Republicans in small groups. By and large, they have found him more approachable than they expected, but much less informed. “Several have been a little bit amazed by the lack of policy knowledge,” Kristol said. “God knows Presidents don’t need to know the details of health-care bills and tax bills, and I certainly don’t, either—that’s what you have aides for. But not even having a basic level of understanding? I think that has rattled people a little bit.” He added, “Reagan may not have had a subtle grasp of everything, but he read the briefing books and he knew the arguments, basically. And Trump is not even at that level.”

When I asked Kristol about the chances of impeachment, he paused to consider the odds. Then he said, “It’s somewhere in the big middle ground between a one-per-cent chance and fifty. It’s some per cent. It’s not nothing.”

The history of besieged Presidencies is, in the end, a history of hubris—of blindness to one’s faults, of deafness to the warnings, of seclusion from uncomfortable realities. The secret of power is not that it corrupts; that is well known. “What is never said,” Robert Caro writes, in “Master of the Senate,” about Lyndon Johnson, “is that power reveals.” Trump, after a lifetime in a family business, with no public obligations and no board of directors to please, has found himself abruptly exposed to evaluation, and his reactions have been volcanic. Setting a more successful course for the Presidency will depend, in part, on whether he fully accepts that critics who identify his shortcomings are capable of curtailing his power. When James P. Pfiffner, a political scientist at George Mason University, compared the White House crises that confronted Nixon, Reagan, and Clinton, he identified a perilous strain of confidence. In each case, Pfiffner found, the President could not “admit to himself that he had done anything wrong.” Nixon convinced himself that his enemies were doing the same things he was; Reagan dismissed the trading of arms for hostages as the cost of establishing relations with Iran; Clinton insisted that he was technically telling the truth. In Pfiffner’s view, “Each of these sets of rationalizations allowed the Presidents to choose the path that would end up damaging them more than an initial admission would have.”

Law and history make clear that Trump’s most urgent risk is not getting ousted; it is getting hobbled by unpopularity and distrust. He is only the fifth U.S. President who failed to win the popular vote. Except George W. Bush, none of the others managed to win a second term. Less dramatic than the possibility of impeachment or removal via the Twenty-fifth Amendment is the distinct possibility that Trump will simply limp through a single term, incapacitated by opposition.

William Antholis, a political scientist who directs the Miller Center, at the University of Virginia, told me that, thus far, the President that Trump most reminds him of is not Nixon or Clinton but Jimmy Carter, another outsider who vowed to remake Washington. Carter is Trump’s moral and stylistic opposite, but, Antholis said, “he couldn’t find a way to work with his own party, and Trump’s whole message was pugnacious. It was ‘I alone can fix this.’ ” Like Trump, Carter had majorities in both chambers, but he alienated Congress, and, after four years, he left the White House without achieving his ambitions on welfare, tax reform, and energy independence.

Oscillating between the America of Kenosha and the America of Mar-a-Lago, Trump is neither fully a revolutionary nor an establishmentarian. He is ideologically indebted to both Patrick Buchanan and Goldman Sachs. He is what the political scientist Stephen Skowronek calls a “disjunctive” President, one “who reigns over the end of his party’s own orthodoxy.” Trump knows that Reaganite ideology is no longer politically viable, but he has yet to create a new conservatism beyond white-nationalist nostalgia. For the moment, all he can think to do is rekindle the embers of the campaign, to bathe, once more, in the stage light. It lifts him up. But what of the public? Does he understand that all citizens will have a hand in his fate?

When Trump’s speech in Kenosha was over, he walked across the stage to sign an executive order. “Get ready, everybody,” he said. “This is a big one.” Since taking office, he had issued twenty-four executive orders, and the signings had become a favorite way of displaying his power. The scope of this order was modest—it merely established studies of visas and imports—but he described it as “historic.”

He uncapped a pen and, just before he signed the order, he said, “Who should I give the pen to? The big question, right?” There was nervous laughter, and he called some local and visiting politicians up to the stage to stand beside him while he signed. Then he said, “This is a tremendous honor for me,” and tried his joke again: “The only question is, who gets the pen?” He held up the signed order to the cameras, as always, pivoting left, then right, and grinned broadly.

He stepped down from the stage and walked along the front row of the audience, shaking hands, before his Secret Service detail escorted him toward Marine One. He was going straight back to Washington. The audience, kept in place until he was safely extricated, milled about awkwardly. The theatrical atmosphere dissipated, leaving behind the remainder of an ordinary Tuesday at work.

I approached a woman who introduced herself as Donna Wollmuth. She was sixty-eight years old, and she worked in Snap-on’s warehouse, packing boxes for shipment. I asked her what she thought of Trump’s comments. “I believe in it,” she said. “And I believe in America. I want the jobs back here.”

At first, I wondered if she was merely repeating Trump’s slogans, but it became clear that she had thought hard about his message. Her story was of the kind that has become a stock explanation for Trump’s rise. For twenty-three years, she operated a sewing machine, making briefs and sportswear at Jockey. When the plant closed, in 1993, and production moved offshore, she found a job at the Chicago Lock factory (“Five years later, they closed”) and then one at Air Flow Technology, making industrial filters. After fourteen years there, she was earning almost seventeen dollars an hour, but in 2015 she was laid off. “I lost my job there because they hired somebody that they could pay seven dollars less. It was a lot of immigrants there. Let’s put it that way. I’m sure you know what I mean.” She didn’t like the way it sounded, but she wanted me to understand. “I’m just so stuck on this immigration thing. I really am, because I’ve lived through it, giving benefits and everything to people that aren’t here legally.”

Wollmuth had almost always voted for Democrats, but she had come to believe that her family—she has seven grandchildren and stepgrandchildren—faced a dark future. When Trump entered the race, Wollmuth was turned off by his antics. “He’s gotta learn to keep his mouth shut,” she said, but his pledge to reënergize American manufacturing was too specific and attractive to ignore. She took a chance on Trump, as did many of her neighbors. After going for Obama by large margins in the previous two elections, Kenosha County sided with Trump, by just two hundred and fifty-five votes out of more than seventy-one thousand cast.

That is a fragile buffer. In late April, Trump promoted the results of a Washington Post/ABC News poll showing that only two per cent of those who voted for him regretted doing so. When I asked Wollmuth if she had any regrets, she made it clear that it was the wrong question. “I don’t want to be disappointed, and I hope he’s really trying,” she said. “I’d like to believe that. I’d like to see it happen. I’ve got mixed emotions with him so far.”

Walking out of Snap-on’s headquarters, through the chanting crowd, I wondered whether Trump could see the protesters from his chopper. He knows the unpredictable potential of a crowd. I remembered something that Sam Nunberg, the Trump campaign adviser, had told me about Trump’s fixation on crowds. “I said to him once, ‘I understand it’s the biggest. Who gives a shit? Who cares at this point? What we care about is votes,’ ” Nunberg said. “And he says, ‘No. It’s got to be.’ Some of it was he was seriously concerned about the country. He also wanted to see where this went and what it was. The crowds and energy showed him it was a movement.”