It wasn’t hard to see, when it began, that it would end exactly the way it has. Donald Trump is America’s willful arsonist, the man who lit the match under the fabric of our constitutional republic.

The duty of the House of Representatives and the Senate, once they certify Joe Biden’s election, is to reconvene, Wednesday night if possible, to impeach the president and then remove him from office and bar him from ever holding office again.

To allow Trump to serve out his term, however brief it may be, puts the nation’s safety at risk, leaves our reputation as a democracy in tatters and evades the inescapable truth that the assault on Congress was an act of violent sedition aided and abetted by a lawless, immoral and terrifying president.

From the moment Trump became the G.O.P. front-runner in 2015, it was obvious who he was and where, if given the chance, he would take America. He was a malignant narcissist in his person. A fraudster in his businesses. A bully in his relationships. And a demagogue in his politics.

He did not have ideas. He had bigotries. He did not have a coalition. He had crowds. He did not have character. He had a quality of confident shamelessness, the kind that offered his followers permission to be shameless, too.

All this was obvious — but was not enough to stop him. America in 2015 had many problems, many of which had gone too long ignored and were ripe for populist exploitation. But by far the biggest problem of that year was that a major political party capitulated to a thug. And the biggest problem of every subsequent year has been that more and more of that party has excused, ignored, forgiven, colluded in and celebrated his thuggery.

Think of Mike Pompeo, our sycophantic secretary of state, who in March 2016 warned that Trump would be “an authoritarian president who ignored our Constitution,” and who, after the election had been called for Biden in November, promised “a smooth transition to a second Trump administration.”

The Republican Party is now walking to the edge of moral irredeemability. I say this as someone who, until 2016, had always voted the straight Republican ticket and who, until this week, had hoped that Republicans would hold the Senate as a way of tilting the Biden administration to the center. I say this also of the party generally, and not of the courageous individual Republicans — Brad Raffensperger, Mitt Romney, Denver Riggleman, Larry Hogan, Ben Sasse (the list is depressingly short) — who have preserved their principles, maintained their honor and kept their heads these past five years.

But there is no getting away from the extent to which leading party members and their cheerleaders in the right-wing media are complicit in creating the political atmosphere in which this Visigothic sacking of the Capitol took place.

The legal hucksters, from Rudy Giuliani to Mark Levin, who promoted demonstrably debunkable claims about electoral fraud, are complicit. All of those supposedly sober-minded conservatives who encouraged the president to “pursue his legal options” (knowing full well they were bunk, but with the assurance that they would settle doubts about the validity of the vote) are complicit. The 126 House Republicans who signed on to the preposterous brief supporting the Texas lawsuit to overturn the election — flicked away in a single paragraph by the Supreme Court — are complicit. Ted Cruz, whom I once described as a “serpent covered in Vaseline” but who turns out to be considerably worse, is complicit. Josh Hawley and the rest of the Senate cynics, who tried to obstruct Biden’s election certification in a transparent bid to corner the market on Trumpian craziness, are complicit. Mike Pence, who cravenly humored Trump’s fantasies right till the moment of constitutional truth, is complicit. (If there’s an argument against Trump’s removal from office, he alone is it.)

Some of these charlatans are now trying to disavow Wednesday’s violence in carefully phrased tweets. But Cruz, Hawley, Pence and the other Bitter-Enders have done far more lasting damage to Congress than the mob that — merely by following their lead — physically trashed it. Broken doors can be fixed. Broken parties cannot.

Above all there is the president, not complicit but wholly, undeniably and unforgivably responsible.

For five years, Republicans let him degrade political culture by normalizing his behavior. For five years, they let him wage war on democratic norms and institutions. For five years, they treated his nonstop mendacity as a quirk of character, not a disqualification for office. For five years, they treated his rallies as carnivals of democracy, not as training grounds for mob rule.

For five years, they thought this was costless. On Wednesday — forgive the cliché, but it’s apt here — their chickens came home to roost.

Every decent society depends for its survival on its ability to be shocked — and stay shocked — by genuinely shocking behavior. Donald Trump’s entire presidency has been an assault on that idea.

There is only one prescription for it now. Impeach the president and remove him from office now. Ban him forever from office now. Let every American know that, in the age of Trump, there are some things that can never be allowed to stand, most of all Trump himself.

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