He is demonstrably unfit for office. What are we waiting for?

The presidential oath of office contains 35 words and one core promise: to “preserve, protect and defend the Constitution of the United States.” Since virtually the moment Donald J. Trump took that oath two years ago, he has been violating it. He has

• repeatedly put his own interests above those of the country. He has
• used the presidency to promote his businesses. He has accepted financial gifts from foreign countries. He has
• lied to the American people about his relationship with a hostile foreign government. He has
• tolerated cabinet officials who use their position to enrich themselves.

To shield himself from accountability for all of this — and for his unscrupulous presidential campaign — he has

• set out to undermine the American system of checks and balances. He has
• called for the prosecution of his political enemies and the protection of his allies. He has
• attempted to obstruct justice. He has
• tried to shake the public’s confidence in one democratic institution after another, including
  • the press,
  • federal law enforcement and the
  • federal judiciary.

The unrelenting chaos that Trump creates can sometimes obscure the big picture. But the big picture is simple: The United States has never had a president as demonstrably unfit for the office as Trump. And it’s becoming clear that 2019 is likely to be dominated by a single question: What are we going to do about it?

The easy answer is to wait — to allow the various investigations of Trump to run their course and ask voters to deliver a verdict in 2020. That answer has one great advantage. It would avoid the national trauma of overturning an election result. Ultimately, however, waiting is too dangerous. The cost of removing a president from office is smaller than the cost of allowing this president to remain.

He has already shown, repeatedly, that

• he will hurt the country in order to help himself. He will damage American interests around the world and
• damage vital parts of our constitutional system at home.

The risks that he will cause much more harm are growing.

Some of the biggest moderating influences have recently left the administration. The

• defense secretary who defended our alliances with NATO and South Korea is gone. So is
• the attorney general who refused to let Trump subvert a federal investigation into himself. The administration is increasingly filled with lackeys and enablers. Trump has become freer to turn his whims into policy — like, say, shutting down the government on the advice of Fox News hosts or pulling troops from Syria on the advice of a Turkish autocrat.

The biggest risk may be that an external emergency — a war, a terrorist attack, a financial crisis, an immense natural disaster — will arise. By then, it will be too late to pretend that he is anything other than manifestly unfit to lead.

For the country’s sake, there is only one acceptable outcome, just as there was after Americans realized in 1974 that a criminal was occupying the Oval Office. The president must go.

Since the midterm election showed the political costs that Trump inflicts on Republicans, this criticism seems to be growing. They have broken with him on foreign policy (in Saudi Arabia, Yemen and Syria) and are anxious about the government shutdown. Trump is vulnerable to any erosion in his already weak approval rating, be it from an economic downturn, more Russia revelations or simply the defection of a few key allies. When support for an unpopular leader starts to crack, it can crumble.

Before we get to the how of Trump’s removal, though, I want to spend a little more time on the why — because even talking about the ouster of an elected president should happen only under extreme circumstances. Unfortunately, the country is now so polarized that such talk instead occurs with every president. Both George W. Bush and Barack Obama were subjected to reckless calls for their impeachment, from members of Congress no less.

So let’s be clear. Trump’s ideology is not an impeachable offense. However much you may disagree with Trump’s tax policy — and I disagree vehemently — it is not a reason to remove him from office. Nor are his efforts to cut government health insurance or to deport undocumented immigrants. Such issues, among others, are legitimate matters of democratic struggle, to be decided by elections, legislative debates, protests and the other normal tools of democracy. These issues are not the “treason, bribery or other high crimes and misdemeanors” that the founders intended impeachment to address.

Yet the founders also did not intend for the removal of a president to be impossible. They insisted on including an impeachment clause in the Constitution because they understood that an incompetent or corrupt person was nonetheless likely to attain high office every so often. And they understood how much harm such a person could do. The country needed a way to address what Alexander Hamilton called “the abuse or violation of some public trust” and James Madison called the “incapacity, negligence or perfidy” of a president.

The negligence and perfidy of President Trump — his high crimes and misdemeanors — can be separated into four categories. This list is conservative. It does not include the possibility that his campaign coordinated strategy with Russia, which remains uncertain. It also does not include his lazy approach to the job, like his refusal to read briefing books or the many empty hours on his schedule. It instead focuses on demonstrable ways that he has broken the law or violated his constitutional oath.

Trump has used the presidency for personal enrichment.

Regardless of party, Trump’s predecessors took elaborate steps to separate their personal financial interests from their governing responsibilities. They released their tax returns, so that any potential conflicts would be public. They placed their assets in a blind trust, to avoid knowing how their policies might affect their own investments.

Trump has instead treated the presidency as a branding opportunity. He has continued to own and promote the Trump Organization. He has spent more than 200 days at one of his properties and billed taxpayers for hundreds of thousands of dollars.

If this pattern were merely petty corruption, without damage to the national interest, it might not warrant removal from office. But Trump’s focus on personal profit certainly appears to be affecting policy. Most worrisome, foreign officials and others have realized they can curry favor with the president by spending money at one of his properties.

Then, of course, there is Russia. Even before Robert Mueller, the special counsel, completes his investigation, the known facts are damning enough in at least one way. Trump lied to the American people during the 2016 campaign about business negotiations between his company and Vladimir Putin’s government. As president, Trump has taken steps — in Europe and Syria — that benefit Putin. To put it succinctly:

The president of the United States lied to the country about his commercial relationship with a hostile foreign government toward which he has a strangely accommodating policy.

Combine Trump’s actions with his tolerance for unethical cabinet officials — including ones who have made shady stock trades, accepted lavish perks or used government to promote their own companies or those of their friends — and the Trump administration is almost certainly the most corrupt in American history. It makes Warren G. Harding’s Teapot Dome scandal look like, well, a tempest in a teapot.

Trump has violated campaign finance law.

A Watergate grand jury famously described Richard Nixon as “an unindicted co-conspirator.” Trump now has his own indictment tag: “Individual-1.”

Federal prosecutors in New York filed papers last month alleging that Trump — identified as Individual-1 — directed a criminal plan to evade campaign finance laws. It happened during the final weeks of the 2016 campaign, when he instructed his lawyer, Michael Cohen, to pay a combined $280,000 in hush money to two women with whom Trump evidently had affairs. Trump and his campaign did not disclose these payments, as required by law. In the two years since, Trump has lied publicly about them — initially saying he did not know about the payments, only to change his story later.

It’s worth acknowledging that most campaign finance violations do not warrant removal from office. But these payments were not most campaign finance violations. They involved large, secret payoffs in the final weeks of a presidential campaign that, prosecutors said, “deceived the voting public.” The seriousness of the deception is presumably the reason that the prosecutors filed criminal charges against Cohen, rather than the more common penalty of civil fines for campaign finance violations.

What should happen to a president who won office with help from criminal behavior? The founders specifically considered this possibility during their debates at the Constitutional Convention. The most direct answer came from George Mason: A president who “practiced corruption and by that means procured his appointment in the first instance” should be subject to impeachment.

Trump has obstructed justice.

Whatever Mueller ultimately reveals about the relationship between the Trump campaign and Russia, Trump has obstructed justice to keep Mueller — and others — from getting to the truth.

Again and again, Trump has interfered with the investigation in ways that may violate the law and clearly do violate decades-old standards of presidential conduct. He

•  pressured James Comey, then the F.B.I. director, to let up on the Russia investigation, as a political favor. When Comey refused, Trump fired him. Trump also repeatedly
• pressured Jeff Sessions, the attorney general, to halt the investigation and ultimately forced Sessions to resign for not doing so. Trump has also
• publicly hounded several of the government’s top experts on Russian organized crime, including Andrew McCabe and Bruce Orr.

And Trump has repeatedly lied to the American people.

• He has claimed, outrageously, that the Justice Department tells witnesses to lie in exchange for leniency. He has
• rejected, with no factual basis, the findings of multiple intelligence agencies about Russia’s role in the 2016 campaign. He reportedly
• helped his son Donald Trump Jr. draft a false statement about a 2016 meeting with a Russian lawyer.

Obstruction of justice is certainly grounds for the removal of a president. It was the subject of the first Nixon article of impeachment passed by the House Judiciary Committee. Among other things, that article accused him of making “false or misleading public statements for the purpose of deceiving the people of the United States.”

Trump has subverted democracy.

The Constitution that Trump swore to uphold revolves around checks and balances. It depends on the idea that the president is not a monarch. He is a citizen to whom, like all other citizens, the country’s laws apply. Trump rejects this principle. He has instead tried to undermine the credibility of any independent source of power or information that does not serve his interests.

It’s much more than just the Russia investigation. He has

• tried to delegitimize federal judges based on their ethnicity or on the president who appointed them, drawing a rare rebuke from Chief Justice John Roberts. Trump has
•  criticized the Justice Department for indicting Republican politicians during an election year. He has
• called for Comey, Hillary Clinton and other political opponents of his to be jailed. Trump has .
• described journalists as “the enemy of the people” — an insult usually leveled by autocrats. He has
• rejected basic factual findings from the
  • C.I.A., the
  • Congressional Budget Office,
  • research scientists and
  • others.
• He has told bald lies about election fraud.

Individually, these sins may not seem to deserve removal from office. Collectively, though, they exact a terrible toll on American society. They cause people to lose the faith on which a democracy depends — faith in elections, in the justice system, in the basic notion of truth.

No other president since Nixon has engaged in behavior remotely like Trump’s. To accept it without sanction is ultimately to endorse it. Unpleasant though it is to remove a president, the costs and the risks of a continued Trump presidency are worse.

What now?

The most relevant precedent for the removal of Trump is Nixon, the only American president to be forced from office because of his conduct. And two aspects of Nixon’s departure tend to get overlooked today. One, he was never impeached. Two, most Republicans — both voters and elites — stuck by him until almost the very end. His approval rating among Republicans was still about 50 percent when, realizing in the summer of 1974 that he was doomed, he resigned.

The current political dynamics have some similarities. Whether the House of Representatives, under Democratic control, impeaches Trump is not the big question. The question is whether he loses the support of a meaningful slice of Republicans.

I know that many of Trump’s critics have given up hoping that he ever will. They assume that Republican senators will go on occasionally criticizing him without confronting him. But it is a mistake to give up. The stakes are too large — and the chances of success are too real.

Consider the following descriptions of Trump:

• “terribly unfit;”
• “erratic;”
• “reckless;”
• “impetuous;”
• “unstable;”
• “a pathological liar;”
• “dangerous to a democracy;”
• a concern to “anyone who cares about our nation.”

Every one of these descriptions comes from a Republican member of Congress or of Trump’s own administration.

They know. They know he is unfit for office. They do not need to be persuaded of the truth. They need to be persuaded to act on it.

.. Democrats won’t persuade them by impeaching Trump. Doing so would probably rally the president’s supporters. It would shift the focus from Trump’s behavior toward a group of Democratic leaders whom Republicans are never going to like. A smarter approach is a series of sober-minded hearings to highlight Trump’s misconduct.

Democrats should focus on easily understandable issues most likely to bother Trump’s supporters, like corruption.

If this approach works at all — or if Mueller’s findings shift opinion, or if a separate problem arises, like the economy — Trump’s Republican allies will find themselves in a very difficult spot. At his current approval rating of about 40 percent, Republicans were thumped in the midterms. Were his rating to fall further, a significant number of congressional Republicans would be facing long re-election odds in 2020.

Two examples are Cory Gardner of Colorado and Susan Collins of Maine, senators who, not coincidentally, have shown tentative signs of breaking with Trump on the government shutdown. The recent criticism from Mitt Romney — who alternates between critical and sycophantic, depending on his own political interests — is another sign of Trump’s weakness.

For now, most Republicans worry that a full break with Trump will cause them to lose a primary, and it might. But sticking by him is no free lunch. Just ask the 27 Republican incumbents who were defeated last year and are now former members of Congress. By wide margins, suburban voters and younger voters find Trump abhorrent. The Republican Party needs to hold its own among these voters, starting in 2020.

It’s not only that Trump is unfit to be president and that Republicans know it. It also may be the case that they will soon have a political self-interest in abandoning him. If they did, the end could come swiftly. The House could then impeach Trump, knowing the Senate might act to convict. Or negotiations could begin over whether Trump deserves to trade resignation for some version of immunity.

Finally, there is the hope — naïve though it may seem — that some Republicans will choose to act on principle. There now exists a small club of former Trump administration officials who were widely respected before joining the administration and whom Trump has sullied, to greater or lesser degrees. It includes

• Rex Tillerson,
• Gary Cohn,
• H.R. McMaster and
• Jim Mattis.

Imagine if one of them gave a television interview and told the truth about Trump. Doing so would be a service to their country at a time of national need. It would be an illustration of duty.

Throughout his career, Trump has worked hard to invent his own reality, and largely succeeded. It has made him very rich and, against all odds, elected him president. But whatever happens in 2019, his false version of reality will not survive history, just as Nixon’s did not. Which side of that history do today’s Republicans want to be on?