THE SECOND impeachment trial of former president Donald Trump accomplished much, and left much still to accomplish.

The House impeachment managers proved beyond doubt that Mr. Trump was guilty of a “disgraceful dereliction of duty.” That was the post-trial assessment of the Republican Senate leader, Mitch McConnell of Kentucky, who said that Mr. Trump waged a “campaign of disinformation and rage” in the weeks leading up to Jan. 6 and then was “practically and morally responsible for provoking” the attack on the Capitol by his followers on that day. Mr. Trump inflamed a violent mob that sought to derail a peaceful transition of power and then refused to calm or call back his supporters as they assaulted police officers and threatened the lives of Vice President Mike Pence and many other officials.

The trial established a vital record for history — and persuaded a bipartisan majority of 57 senators to vote to convict Mr. Trump. Among them were seven Republicans, whose commitment to principle should be saluted: Richard Burr (N.C.), Bill Cassidy (La.), Susan Collins (Maine), Lisa Murkowski (Alaska), Mitt Romney (Utah), Ben Sasse (Neb.) and Patrick J. Toomey (Pa.). As profiles in courage, they join Rep. Liz Cheney (R-Wyo.), who risked her House leadership position to repudiate Mr. Trump’s betrayals, and Rep. Jaime Herrera Beutler (R-Wash.), who bore witness to Mr. Trump’s abhorrent behavior on Jan. 6 even as other Republicans fell into line.

Mr. McConnell, his assessment of Mr. Trump’s misbehavior notwithstanding, joined with 42 other Republicans in voting to acquit. He said he does not believe the Constitution gives the Senate the power to try a former officer, a view we find implausible but one that some scholars endorse. There is a way for Mr. McConnell to square this circle: immediately join in sponsoring a resolution of censure. Though it would be a milder sanction than conviction by two-thirds of the Senate, there would be value in requiring every senator to go on the record with regard to Mr. Trump’s repulsive and dangerous actions.

Congress’s duty does not end there, however. Mr. Trump’s guilt is clear, but many questions about the events of Jan. 6 remain unanswered. They should be investigated, not least because of the threat that Mr. Trump continues to pose. Congress should immediately empanel a committee or commission to conduct an investigation.

Such an inquiry would seek testimony from those around Mr. Trump on Jan. 6, such as then-White House Chief of Staff Mark Meadows. How did the White House process widespread reports that Trump fanatics were planning violence on Jan. 6? How, precisely, did Mr. Trump respond as he watched the riot unfold? What, if any, conversations took place between the White House and the Pentagon about sending in the National Guard?

It might take time to compel former administration officials such as Mr. Meadows or Marc Short, Mr. Pence’s former chief of staff, to testify. But it would be worth it. Mr. Trump’s unsuitability for any role in public life is indisputable, thanks in part to the masterful work of the impeachment managers. But the full history remains to be uncovered.

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