President Trump’s efforts to remain in office in defiance of democracy cannot be allowed to go unanswered, lest they invite more lawlessness from this president or those who follow.

The attack on the Capitol on Wednesday was not a spontaneous eruption of violence. It was the culmination of a campaign waged by the president of the United States and his allies in Congress and the right-wing media to overturn the results of a free and fair election that began even before the ballots began to be counted on Election Day.

That campaign involved a barrage of lies about the integrity of the voting process from the president, his allies and other elected Republicans. It included farcical legal challenges that were laughed out of court even as they sowed doubt in the minds of a majority of Republicans about whether Joe Biden won fairly. It involved the president and his allies strong-arming state election officials to change the vote count outright. When it all failed, the president held a rally on the National Mall and sent the angry crowd to march on the Capitol and stop Congress from declaring Mr. Biden the winner of the presidency. The riot came at the cost of at least five lives and shook the confidence of the nation and the world in the stability of American democracy.

Each of these efforts amounts to an unprecedented assault on the rule of law. Taken together, they constitute a crime so brazen that it demands the highest form of accountability that the legislature can deliver. As regrettable as this moment is for the nation, there is no other option but to vote to impeach the president for a second time.

Mr. Trump began undermining November’s election before the first vote was cast. Throughout the spring and summer, as the pandemic forced states to be more flexible with mail and absentee voting, he claimed repeatedly and without evidence that mail-in balloting would be rife with fraud.

Then, after it was clear Mr. Biden was the victor, and after weeks of public and private attempts to get states to change their vote totals and deliver him a second term, the president encouraged his supporters to converge on Washington on Jan. 6. (“Be there, will be wild!” he tweeted.) Tens of thousands of them, from all over the country, answered his call.

Mr. Trump took to the stage and gave perhaps the most un-American speech ever uttered by a president.

“We will not take it anymore,” Mr. Trump told the crowd. “We will stop the steal.”

“States want to revote. The states got defrauded. They were given false information. They voted on it. Now they want to recertify,” Mr. Trump said to cheers. “They want it back. All Vice President Pence has to do is send it back to the states to recertify, and we become president.”

“Fight for Trump!” the crowd bellowed.

Mr. Trump said that he’d just spoken to the vice president, who was due to oversee the ceremonial counting of electoral votes. “I said: ‘Mike, that doesn’t take courage. What takes courage is to do nothing — that takes courage.’ And then we’re stuck with a president who lost the election by a lot, and we have to live with that for four more years. We’re just not going to let that happen.”

“We’re going to walk down, and I’ll be there with you, we’re going to walk down, we’re going to walk down,” Mr. Trump said, “to the Capitol, and we’re going to cheer on our brave senators and congressmen and -women, and we’re probably not going to be cheering so much for some of them.” He continued: “Because you’ll never take back our country with weakness. You have to show strength, and you have to be strong. We have come to demand that Congress do the right thing and only count the electors who have been lawfully slated, lawfully slated.”

“We fight. We fight like hell,” the president said. “If you don’t fight like hell, you’re not going to have a country anymore.”

With that, the crowd struck off and some of the president’s loyalists stormed the Capitol.

The charges against Mr. Trump are clear: inciting an insurrection. The House could give him fair consideration without the lengthy hearings it required to impeach him in December 2019 after he strong-armed the Ukrainian president. The evidence now is not secondhand accounts of meetings and phone calls. The offenses occurred in public for weeks and then live on national television.

Significant support from Republicans would be necessary to achieve the two-thirds majority in the Senate required for a conviction. But the deadly attack on Congress finally seems to have shaken some of them from their reflexive backing of the president who incited it. Senators were driven out of their own chamber, and into hiding, while they were in the middle of performing their constitutional duty of counting the electoral votes.

Mr. Trump may not have called directly for this behavior, but there is no question that he encouraged it and then refused for hours to condemn it, even as the whole world watched in horror. When he finally asked for rioters to stop and go home, he continued to claim the election had been stolen.

So far, among Republicans, only Senator Ben Sasse of Nebraska, who described the president’s behavior as “wicked,” has said he would consider impeachment. Others are said to be privately discussing voting for it. Senators Lisa Murkowski of Alaska and Pat Toomey of Pennsylvania have called on the president to resign. If Republican senators refuse to convict Mr. Trump, they would go on the record — for their constituents to see and reconcile — defending a man who was happy to put their lives, and the nation’s democratic future, at risk for nothing but his own quest to hold on to power.

The arguments against impeachment — that it could actually sow more division or further embolden Mr. Trump and his allies politically, that it could distract from Mr. Biden’s agenda in his first several weeks in office, that the Senate may ultimately fail to convict — are worth considering. There could be more unrest and even violence. In many ways, it would be easier to let Mr. Trump leave office and attempt to consign the storming of the Capitol to the past.

But, ultimately, there can be no republic if leaders foment a violent overthrow of the government if they lose an election.

Mr. Trump is not the only person at fault. Many Republican lawmakers riled up his supporters for weeks with false claims of election rigging and continued to object to the electoral vote even after the attack. The 14th Amendment bars from office any federal or state lawmaker who has “engaged in insurrection or rebellion” or given “aid or comfort” to those who have. Congressional leaders will need to reckon with which of their colleagues require censure for their actions, and perhaps even expulsion.

Any and all rioters who broke laws on Wednesday need to be identified and prosecuted. Attempting insurrection is as serious a crime as there is in a self-governing republic. As more of the rioters are arrested, it will also be essential to get to the bottom of how they were allowed to wreak havoc and yet, for the most part, walk away unscathed. That will require investigations by both Congress and the Justice Department.

Yet it can’t be lost that the violence on Wednesday was the nadir of a coordinated, relentless campaign to cast doubt on the strength of American democracy. In the end, the driving force behind the lies, the chaos and the bloodshed of the past few days and weeks is Mr. Trump. As long as he is not held fully to account, any future chief executive might feel equally unbound by a lawless precedent.

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