THE SENATE will begin considering Tuesday whether to convict Donald Trump following the House’s unprecedented second impeachment of the now-former president. Mr. Trump’s lawyers, as well as many Republicans, deny that the proceedings are legitimate. They are wrong. The Senate must hold its trial, and the right vote is for conviction.

The House was able to impeach Mr. Trump quickly in the final days of his presidency because he betrayed the nation on live television. The House impeachment managers’ brief is damning, even though it reveals little that was not already in the public record.

After Mr. Trump lost the Nov. 3 presidential election, he conducted a persistent campaign of lies alleging that Joe Biden’s victory was fraudulent. His campaign escalated after he failed in court; he suggested Senate Republicans should “fight to the death.” He asked supporters to descend on Washington on Jan. 6, the day Congress was to count electoral votes. Some of those supporters responded by planning to attack the Capitol.

On the morning of Jan. 6, Mr. Trump instructed the crowd to go to the Capitol and warned, “If you don’t fight like hell, you’re not going to have a country anymore.” Supporters screamed, “Take the Capitol right now!” That is what they did after Mr. Trump stopped speaking. Mr. Trump watched as a mob chanting “Hang Mike Pence” stormed the building, resulting in multiple deaths, the interruption of the electoral vote counting and the desecration of the nation’s seat of government. Some in the mob reported that they were following Mr. Trump’s directions. Mr. Trump eventually issued meek statements designed as much to justify the mob’s rage as to pacify it.

Mr. Trump’s lawyers claim that the former president was just exercising his First Amendment rights. But public officials are accountable for the things they say; Mr. Trump would have fired any member of his Cabinet who had, say, publicly denounced him. Mr. Trump is responsible for whipping extremists into a frenzy with lies, encouraging violence and directing those extremists to the chambers in which members of Congress were overseeing the transfer of power. He betrayed his oath to faithfully execute his duties and defend the Constitution; indeed, he disrupted the core operations of the constitutional system.

Many Republicans avoid saying much about Jan. 6, instead claiming that the Senate cannot try to convict Mr. Trump after he has left office. This is a convenient but faulty interpretation. The Constitution contemplates two potential punishments for impeached officials: removal and barring from further service. If former officials could not be impeached and convicted, those facing impeachment could resign quickly and avoid being blacklisted. Historically, Congress has avoided this nonsensical view. What’s more, the House impeached Mr. Trump while he was still in office, and the Constitution states unambiguously that “the Senate shall have the sole Power to try all Impeachments.”

Early on Jan. 6, The Post's Kate Woodsome saw signs of violence hours before thousands of former president Donald Trump loyalists besieged the Capitol. (Joy Yi, Kate Woodsome/The Washington Post)

Senators must not hide behind fig-leaf arguments. They should listen to the nearly 400 congressional staffers who wrote them a letter about the trauma they endured on Jan. 6, begging them to convict Mr. Trump. And they should think about the precedent they set. As the House managers put it, “Failure to convict would embolden future leaders to attempt to retain power by any and all means — and would suggest that there is no line a President cannot cross.”

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