The peaceful transfer of presidential power through free and fair elections is the crowning glory of American democracy. It concretizes the people’s will, conferring legitimacy, assuring stability. President Trump may have finished second in the popular vote, but he is the legitimate president. In the normal course of events, his mismanagement of the nation’s affairs would be left for the electorate to repudiate, through support of a challenger in a primary race or, failing that, in the general election.

But the course of events is not normal. Mr. Trump campaigned as an iconoclast, but it became clear early in his administration that his disruptiveness was aimed less at bringing fresh thinking to bear on stale policymaking than at assaulting the vital institutions of governance themselves. He has attacked the legitimacy of law enforcement, of intelligence agencies, of Congress and of the courts — of anyone he judges to threaten him politically.

For nearly three years, public-spirited people have debated whether each instance of executive overreach by Mr. Trump and his lieutenants went far enough to require the traumatic recourse of an impeachment inquiry. They have wondered at what point the checks and balances of American governance might have to be restored by means of the most radical check of all.

That point has now been reached.

The American people have learned over the past week that Mr. Trump, during a July phone call, pressed the president of Ukraine, Volodymyr Zelensky, to investigate Joe Biden, one of his leading political rivals, according to a written summary of the conversation released by the White House. What’s more, Mr. Trump offered the assistance of the Justice Department in that investigation. These facts are not in dispute, which is why some of the president’s die-hard defenders are trying to dismiss the conversation as an inconsequential instance of the president’s bad judgment.

But it was so much more dangerous than that. A president’s use of his power for his own political gain, at the expense of the public interest, is the quintessence of an impeachable offense. It was, in fact, one of the examples the Constitution’s framers deployed to explain what would constitute “high crimes and misdemeanors,” the standard for impeachment.

Have other presidents conducted foreign policy with re-election in mind? Of course. But there is no known precedent for a president pressuring a foreign nation to tear down a political rival. (As a candidate in 1968, Richard M. Nixon tried to sabotage peace talks to end the Vietnam War, but the details didn’t become public knowledge until decades later.)

Have other presidents conducted foreign policy with re-election in mind? Of course. But there is no known precedent for a president pressuring a foreign nation to tear down a political rival.

Mr. Trump appears to have applied more than just verbal pressure. Just days before the call with President Zelensky, Mr. Trump froze nearly $400 million in military aid to Ukraine, aid that Congress had judged to be in America’s national security interest. He released those funds weeks later, and only under intense bipartisan pressure from Congress. Even the president’s reliable ally Mitch McConnell, the Senate majority leader, has said he did not receive an explanation for why Mr. Trump chose to withhold those funds.

The president has insisted that he raised the matter with Mr. Zelensky because Mr. Biden, as vice president, had engaged in criminal conduct. Mr. Biden has denied that; Mr. Trump has provided no evidence; and previous investigations have found no evidence of wrongdoing. But consider the hypothetical that Mr. Trump was correct about Mr. Biden. Would that legitimize the president’s behavior? No. If the president had evidence, his White House counsel should have shared it with the Department of Justice and let the F.B.I. do its job, in coordination with Ukrainian counterparts.

White House aides appear to have recognized that Mr. Trump egregiously overstepped, and to have tried to cover up his actions. According to the complaint filed in August by a whistle-blower in the intelligence community and released publicly on Thursday morning, there was a discussion among “White House lawyers about how to treat the call because of the likelihood, in the officials’ retelling, that they had witnessed the president abuse his office for personal gain.” At the direction of White House lawyers, the whistle-blower says, these officials “intervened to ‘lock down’ all records of the phone call, especially the word-for-word transcript that was produced.” And “this was ‘not the first time’” White House officials had done this, according to the complaint.

Some of Mr. Trump’s defenders assert that no criminal statute prevents a president from soliciting foreign interference in American elections. But the law is clear that impeachment does not require a crime. In fact, the absence of a criminal statute to restrain this sort of abuse of authority only reinforces the need for Congress to act in accordance with the aims of the framers of the Constitution. As Alexander Hamilton wrote in Federalist No. 65, impeachment was provided as a response not just to crimes but to acts that were an “abuse or violation of some public trust.” During this administration, Americans have discovered to their sorrow the degree to which past presidents were constrained not by specific laws but only by tradition, character and an understanding of the framers’ intent. Mr. Trump has proved immune to such considerations.

Of course, the president has committed previous offenses that many critics argued justified an impeachment inquiry months if not years ago. During the 2016 campaign, he appears to have violated federal election law by directing his personal lawyer Michael Cohen to pay $280,000 in hush money to two women who say they had sex with Mr. Trump. Mr. Cohen testified that Mr. Trump continued to reimburse him for making those payments into 2017, after Mr. Trump became president.

In office, he has also repeatedly sought to obstruct federal investigations. And his companies – which he has refused to divest or place in a blind trust – actively solicit business from foreign governments and leaders. Those governments have spent vast sums at Trump properties, enriching the president in possible violation of the emoluments clause of the Constitution, which prohibits foreign gifts.

But an impeachment inquiry was not necessary to deal previously with those transgressions, because the system was working: The courts were dealing with some charges, and the special counsel overseeing the Russia investigation, Robert Mueller, with others. Trump lieutenants were going to prison for their crimes, and despite various efforts by the administration to suppress the truth, an aggressive press ensured the American people learned enough about the dark dealings of Mr. Trump and his associates to inform their decisions in the next presidential election.

White House aides appear to have recognized that Mr. Trump egregiously overstepped, and to have tried to cover up his actions.

This board has made clear its own view of Mr. Trump’s unfitness for his office. We have opposed Mr. Trump not only because of his personal transgressions, divisiveness and dishonesty, but also because of the substance of many of his policies — on the environment, immigration, taxes, trade and other matters. But provided Mr. Trump was acting within the law, he had the absolute right to pursue his chosen course and be judged upon it by the electorate, one way or another, in 2020.

The disclosures about the president’s pressure on Ukraine have changed that picture. They have revealed Mr. Trump to be working to subvert the 2020 election, undermining the proper electoral check on presidential misbehavior. The Constitution provides only one fail-safe in such a situation, and that’s why the House was right this week to announce a formal impeachment inquiry, coordinated by the Judiciary Committee.

After all, Americans have seen this playbook before. During the 2016 campaign, Mr. Trump called on Russia to find emails he hoped would embarrass Hillary Clinton: “Russia, if you're listening, I hope you're able to find the 30,000 emails that are missing,” he bellowed then at a campaign news conference in Florida. Mr. Mueller subsequently showed that Russian agents tried to hack into Mrs. Clinton’s personal servers that same day. He eventually secured the indictment of 12 Russian agents in a hacking scheme, and more than a dozen more Russians in a disinformation campaign. They were trying to divide Americans and help Mr. Trump win.

Now, as president, Mr. Trump evidently feels free to demand such interference directly. In fact, Mr. Trump spoke to the Ukrainian president the day after Mr. Mueller had testified to Congress about the magnitude of Russian interference, its continuing menace and Mr. Trump’s efforts to obstruct the investigation. That Mr. Trump was not dissuaded by the response to Mr. Mueller’s findings from seeking political aid from another foreign source suggests he has learned nothing except that he is free to try anything — that a president may use the office as he chooses to promote his re-election.

We don't have to guess at what he believes. In July, he said it out loud, telling a group of teenagers and young adults that under Article II of the Constitution, "I have the right to do whatever I want as president."

During an impeachment inquiry, the Judiciary Committee has enhanced power to obtain documents from the executive branch and to compel the testimony of the president’s aides. The theory is that the House is dealing with a matter both momentous and urgent, and that in doing so it must operate more like a federal court than an oversight body. That may help Congress overcome Mr. Trump’s past refusals to let it perform its oversight function. “We’re fighting all the subpoenas,” Mr. Trump said in April.

Among the Democrats, some voices are already clamoring for the House to rush to judgment, and perhaps even to narrow its focus to the Ukraine incident. Those would be mistakes. The House now has a duty not to use an impeachment inquiry to seek political advantage but to protect the integrity of the next election by using its powers to conduct a methodical and fair investigation of impeachable behavior.

That Mr. Trump was not dissuaded by the response to Mr. Mueller’s findings from seeking political aid from another foreign source suggests he has learned nothing.

The Judiciary Committee can, and should, seek to require the appearance of presidential aides who have previously claimed immunity from testimony, like Don McGahn, the former White House counsel. It can, and should, seek to compel the disclosure of documents the White House has claimed to be shielded by executive privilege or grand jury protections.

Yet much of Mr. Trump’s behavior should remain outside the scope of the inquiry. The founders intended impeachment as a remedy for committing treason, bribery or high crimes and misdemeanors. While the exact meaning of the last phrase ultimately rests on the judgment of the House, lawmakers would be wise to construe it narrowly, as concerning the same type of conduct as treason and bribery: placing private above public interest.

That is the difference between the justified effort to remove President Nixon from office, for misconduct that amounted to an assault on the integrity of the political system and the rights of private citizens, and the unjustified and unpopular impeachment of President Bill Clinton, for lying under oath about an affair. This is not the moment to seek to investigate Mr. Trump for tax fraud, unless it is tied to impeachable conduct.

It is quite possible, though by no means assured, that an impeachment inquiry will produce political benefits for Mr. Trump. He and many of his supporters draw energy and a sense of purpose from conflict. They relish defining themselves in opposition to enemies real and imagined. Further, weary of bickering in Washington and anxious about paying for health care or housing or schooling or wars without end, many Americans may choose to tune out.

The imperative of constitutional accountability outweighs such fears. Mr. Trump is testing the norms and limits of the American system of government. He has left Congress no other recourse than considering impeachment to prevent future presidents from emulating and even expanding upon his piratical application of executive power.

Just three times before in American history have presidents been subject to impeachment inquiries. The first time, in 1868, when Andrew Johnson was prosecuted by Congress for defying an act meant to limit his constitutional powers, this board deplored Mr. Johnson’s behavior but opposed impeachment, arguing that the matter should be left to the voters. (Mr. Johnson’s position, that it was within his power to fire the secretary of war despite a law intended to constrain him, was ultimately affirmed by the Supreme Court.)

The third time, in 1998, this board supported an impeachment inquiry into charges against Mr. Clinton, citing “the need to have those charges resolved in an open, orderly way.” After the inquiry, the board supported censure rather than impeachment as the appropriate punishment for Mr. Clinton’s transgression.

In between — the second time, in 1973 — this board urged President Nixon to resign rather than submit to the “agony” of an impeachment inquiry that would otherwise be necessary because of “his deliberate violations of the letter and the spirit of the Constitution.” And it concluded that if he would not resign, the impeachment process “would validate the Constitution’s procedure for restraining a lawless president” and “leave Mr. Nixon’s partisans satisfied that he had received due process.”

That last objective is a proper one, yet a hard one to achieve, particularly in this era, when political factions feel entitled to their own facts and so many lawmakers confuse party loyalty with patriotism. Already, Democratic and Republican groups are raising funds off the news of an impeachment inquiry, squaring off to alternate as offense and defense, as though this is all just a lucrative game for insiders. That such behavior is not surprising makes it no less repulsive.

The decision to impeach a president is inherently political, in the sense — the noble sense — that it must be made in the public interest. But it should never be political in the narrow sense of being dictated by the latest poll or the next election. This is a moment for political courage. Americans deserve a government devoted to addressing their real problems. But to get that, they need a government balanced as the founders intended, with free and fair elections and a president checked by Congress from the selfish exercise of extraordinary power. Mr. Trump has disparaged and degraded the institutions of American governance, and it is now time for them, in historic rebuke, to demonstrate the majesty of representative democracy.