Portman opposed Trump's attempt to overturn the election results, and did not back a last-ditch effort by Trump's Republican allies in Congress to object to the formal counting of the electoral votes from swing states in which Biden defeated Trump. Portman said, "I cannot support allowing Congress to thwart the will of the voters" and voted against the objections. Congress's counting of the electoral votes was interrupted by a pro-Trump mob that attempted an insurrection at the Capitol; Portman said Trump "bears some responsibility" for the attack. After Trump was impeached by the House of Representatives for incitement of insurrection, Portman joined most Republican senators in an unsuccessful motion to dismiss the charges and avoid a Senate impeachment trial on the basis that Trump's term had expired and he had become a private citizen. On February 13, 2021, Portman voted to acquit Trump on charges of inciting the January 6 attack on the Capitol.