In summary, the answer to "Can a US President, after impeachment and removal, be re-elected or re-appointed?" was "Yes, unless the Senate votes by simple majority to add the penalty of disqualification to a removal from office."
Suppose a President can see that such a vote is coming and will pass, shortly before an election. Can that President resign just before the vote in order to effectively avoid the disqualification penalty?
SHORT ANSWER
Suppose a President can see that such a vote is coming and will pass, shortly before an election. Can that President resign just before the vote in order to effectively avoid the disqualification penalty?
Probably yes.
But, there is no historical precedent for this happening. Nixon resigned before the House voted to impeach him, not midway into the impeachment proceedings. Neither Andrew Jackson nor Bill Clinton resigned prior to not being convicted on the basis of a U.S. House impeachment.
Several federal judges and one cabinet official, however, have resigned midway through impeachment proceedings prior to being convicted, and in those cases, the case was dismissed and no judgment was entered by the U.S. Senate, so they were not disqualified from holding future federal public offices.
LONG ANSWER
The pertinent provisions of the U.S. Constitution include the following:
Article I, Section 2, Clause 5:
The House of Representatives shall chuse their Speaker and other Officers; and shall have the sole Power of Impeachment.
Article I, Section 3, Clauses 6 and 7:
6: The Senate shall have the sole Power to try all Impeachments. When sitting for that Purpose, they shall be on Oath or Affirmation. When the President of the United States is tried, the Chief Justice shall preside: And no Person shall be convicted without the Concurrence of two thirds of the Members present.
7: Judgment in Cases of impeachment shall not extend further than to removal from Office, and disqualification to hold and enjoy any Office of honor, Trust or Profit under the United States: but the Party convicted shall nevertheless be liable and subject to Indictment, Trial, Judgment and Punishment, according to Law.
Article II, Section 4:
The President, Vice President and all civil Officers of the United States, shall be removed from Office on Impeachment for, and Conviction of, Treason, Bribery, or other high Crimes and Misdemeanors.
Article II, Section 2, Clause 3:
The Trial of all Crimes, except in Cases of Impeachment, shall be by Jury; and such Trial shall be held in the State where the said Crimes shall have been committed; but when not committed within any State, the Trial shall be at such Place or Places as the Congress may by Law have directed.
The key language is in Article I, Section 3, Clause 7 of the U.S. Constitution which states in the pertinent part that:
Judgment in Cases of impeachment shall not extend further than to removal from Office, and disqualification to hold and enjoy any Office of honor, Trust or Profit under the United States[.]
This means that a President who is impeached by the House and convicted by the U.S. Senate may be prohibited from holding any federal office from President to dogcatcher in the future.
But, this can only be done in a "judgment" of the U.S. Senate in connection with an impeachment based upon a conviction in the U.S. Senate following a House impeachment, which has never happened.
The history of the impeachment language and the limitation to removals from office, suggest that only a person who is current serving in office may be impeached. Otherwise, the proceeding would be invalid as moot, and would be dismissed (as it has been in the case of many judges who have resigned after investigations are initiated or after a House impeaches but prior to a conviction of impeachment).
A U.S. Senate ruling that someone is disqualified from holding future office can only be entered in a judgment of conviction for impeachment, so cannot apply to a past President. If this were done it would probably be an invalid "Bill of Attainder" or "Ex Post Facto" law. See U.S. Constitution, Article I, Section 9, Clause 3 ("No Bill of Attainder or ex post facto Law shall be passed").
And, the U.S. Senate can't pass a law unilaterally, or enter a judgment convicting someone on an impeachment unless the House initiates the proceeding.
There is no precedent concerning whether if someone who was convicted by the U.S. Senate and removed from office based upon an impeachment initiated by the U.S. House, in which the judgment did not disqualify the person impeachment from holding future federal public offices, the U.S. Senate could amend its judgment later on to also disqualify the person so removed from office from holding further public office.
I suspect that if the question were presented that the federal courts would hold that the amendment of the impeachment judgment was not valid because the word "judgment" implies an immediate ruling upon a case and not a perpetual right to hold the person subject to the judgment in limbo regarding the consequences of his impeachment conviction.
That is, in effect, what President Nixon did. He resigned when the House was preparing articles of impeachment which seemed likely to pass. His resignation stopped the impeachment process. Of course, no one can say what the Senate would have done had he not resigned, but many people expected a conviction and removal from office.
Had Nixon been in his first term as President, his resignation would have left him legally able to run for a second term later (unlikely as that might have been, politically). Even as it was, he was legally able to run for Congress later (although he never did). Had he been removed from office and had the Senate added disqualification to removal, he would have been barred from so running, or from being appointed to a Federal Judgeship. Not that these would have been likely events in any case, but that is the legal effect.
The case of William Belknap indicates that impeachment and trial need not end with the resignation. He was impeached by the House after his resignation, and was tried and acquitted by the Senate (largely because some of the Senators didn't feel they had jurisdiction any longer). I'm assuming the reason the trial was held was so Belknap might be disqualified from holding future office.
You asked:
Suppose a President can see that such a vote is coming and will pass, shortly before an election. Can that President resign just before the vote in order to effectively avoid the disqualification penalty?
Then I asked
Are you considering a resignation before the Senate votes on whether to convict, or after that vote but before a second vote on whether to disqualify?
You responded:
The latter, principally, assuming a practical gap between the two.
In that case, the answer is clearly no, the impeached president cannot resign at that point, because the president has already been removed from office by the Senate's vote for conviction. One cannot resign from an office one does not hold.
Yes. But there is nothing to stop the House re-impeaching the newly elected President and the Senate convicting.
