WASHINGTON—Democrats argued Donald Trump “assembled, inflamed and incited” the attack against the Capitol in a last-ditch effort to overturn the result of the election, relying on Mr. Trump’s own words to make their case in the former president’s second impeachment trial.

Impeachment managers said that Mr. Trump spent months leading up to the election convincing his supporters that the only way he could lose is if the vote were rigged, then urged his supporters to march to the Capitol knowing the potential for violence. Democrats pointed to statements by several rioters who said they believed they were storming the Capitol at Mr. Trump’s direction.