In an early morning tweet that appeared to seize on a statement from two members of the Senate Judiciary Committee about Mr. Comey’s handling of the inquiry, Mr. Trump complained of “a rigged system,” returning to his grudge against the former F.B.I. chief.

While the president had initially cited Mr. Comey’s conduct in the Clinton investigation as the reason for his ouster in May, he later conceded that he had been stewing about Mr. Comey’s focus on possible collusion between the Trump campaign and Russia to sway the election when he decided to dismiss him.