Impeachment
An interesting consideration is that an ex-President does not have the White House legal counsel or the Justice Department to help defend himself. Or does he? It would be odd, since there is a new President who is their boss. The new President should really volunteer the resources for the old one, though.
We should perhaps distinguish between the two cases of a President who resigns in the middle of an impeachment and the President whose term ends naturally. A reasonable position might be that the proceedings continue if the President resigns in the middle of them, but expire if his regular term expires. I might write on this.
It is not altogether ridiculous that a President be impeached after he is no longer President. It is ridiculous to being proceedings when somebody is no longer an officer of the United States, to be sure. This is a difference between the United States and England, where impeachment is a criminal proceeding designed to punish someone the legislature cannot entrust to the justice of the King's courts, which are not independent. Thus, the example of Warren Hastings does not apply. But what if proceedings are begun when the person is an officer, but he resigns to avoid being convicted and losing his ability to serve in the future, when the political climate has changed? In such a case, it seems reasonable that we would not want his resignation to stop the proceedings. That was the case with Governor Pa Ferguson in Texas in the 1920's. Trump's case is neither of these. He was impeached while President--twice-- but his term came to its natural end. Could the Senate then try him after his term expired? Note that if this is so, then the Senate could have a trial based on either impeachment--- the first, in 2020 on charges of corrupt dealings with the Ukraine, or the second, in 2021, on charges of inciting rebellion. This is not a criminal proceeding, so double jeopardy does not apply.
Pa Ferguson's Impeachment in Texas
Ferguson v. Maddox, the Pa Ferguson Texas case from the 1920's, and the Impeachment After Leaving Office article that discusses it. Ferguson resigned after his impeachment but before his Senate trial. He was impeached after he started a big fight with the President of the University of Texas. In 1924 he wanted to run again, but his wife, Ma Ferguson, ran in his place because the Texas Supreme Court ruled that his Senate trial was valid and disqualified him from office. She ran against the KKK's candidate and won.
When Belknap's case was exhibited to the Senate by the Housemanagers, it was framed as articles of impeachment against "WilliamW. Belknap, late Secretary of War."' That first sentence wouldprove the entirety of the issue for a minority, but a determinativenumber, of senators. --Jonathan Turley, "Senate Trials and Factional Disputes: Impeachment As a MadisonianDevice," Duke Law Journal 49, no. 1 (October 1999): 1-146
References
"Review: Impeachment, Attainder, and a True Constitutional Crisis: Lessons from the Strafford Trial," Craig S. Lerner, The University of Chicago Law Review, Autumn, 2002, Vol. 69, No. 4 (Autumn, 2002), pp. 2057-2101 https://www.jstor.org/stable/1600627.
