Yesterday, at The White House:
Reporter: "Is the President saying if he doesn't win this election that he will not accept the results unless he wins?"
McEnany: "The President has always said he'll see what happens and make a determination in the aftermath."
He has no constitutional authority not to accept results of the election as his first term ends four years after it began:
The executive Power shall be vested in a President of the United States of America. He shall hold his Office during the Term of four Years...
And the process for the next term is outlined in the 12th Amendment:
The Electors shall meet in their respective states and vote by ballot for President and Vice-President, one of whom, at least, shall not be an inhabitant of the same state with themselves; they shall name in their ballots the person voted for as President, and in distinct ballots the person voted for as Vice-President, and they shall make distinct lists of all persons voted for as President, and of all persons voted for as Vice-President, and of the number of votes for each, which lists they shall sign and certify, and transmit sealed to the seat of the government of the United States, directed to the President of the Senate;-The President of the Senate shall, in the presence of the Senate and House of Representatives, open all the certificates and the votes shall then be counted;-The person having the greatest Number of votes for President, shall be the President, if such number be a majority of the whole number of Electors appointed;[Emphasis added.]
And so on. The rest of the amendment outlines the process by which the Congress chooses the next president in the event there isn't a majority of electoral votes.
Trump simply does not have any constitutional authority in the matter. If someone else garners a majority of electoral votes, he's out.
For years our friends in the GOP (Senator Pat Toomey, for example) criticized a certain previous administration for "executive overreach." Where is Toomey's outrage over Trump's ultimate executive overreach (threatening to ignore the outcome of the election)?