The impeachment managers hurt their case by blaming only Mr. Trump for earlier clashes. “ Donald Trump, over many months, cultivated violence,” said Stacey Plaskett, the delegate for the Virgin Islands. But often those events were showdowns between left and right, with both seeking trouble. “When darkness fell,” the Washington Post reported after one melee, “the counterprotesters triggered more mayhem as they harassed Trump’s advocates, stealing red hats and flags and lighting them on fire.”

Yet there’s no defense for Mr. Trump’s conduct on Jan. 6 and before. Mitch McConnell is reportedly telling his GOP colleagues that the decision to convict or acquit is a vote of conscience, and that’s appropriate. After the Electoral College voted on Dec. 14, Mr. Trump could have conceded defeat and touted his accomplishments.

Now his legacy will be forever stained by this violence, and by his betrayal of his supporters in refusing to tell them the truth. Whatever the result of the impeachment trial, Republicans should remember the betrayal if Mr. Trump decides to run again in 2024.