Constitution (Section 2, Clause 1), which provides: ... shall have Power to grant Reprieves and Pardons for Offenses against the United States, except in Cases of impeachment.
I am no lawyer, but it seems to me that the House of Representatives could issue articles of impeachment against Trump, and for those accusations included in the article, Trump would not have the power to pardon himself, even if he might have that power otherwise (which everyone seems to doubt.) The fact that the proceedings would become moot after inauguration day so that the Senate would not get to conduct its trial is irrelevant. The Constitution says “Impeachment” , not “conviction.”