Democrats won it on demographics and vote fraud. Trump has done nothing so far to stop either.
What can he do? He's not emperor. He at least called out the ballot stuffing, repeated voting, illegals voting, etc. which is far more than any other Republican president would have ever done.
President Trump can't do much about the multiple election machines across the country. These absolutely need local oversight. Republicans need to be at every precinct, watching over everything like hawks.