The difference is that with Bush you have hanging chads and a court decision that after the votes were counted would have probably come out differently, and a concerted political effort to turn that to their advantage.

The republican party just literally spent months on questioning the election in places like Arizona with no evidence of any fraud, and there's plenty of documentation on how (almost always republican) politicians use lies to get people to not vote: https://lawyerscommittee.org/wp-content/uploads/2015/07/Dece...

Basically, if you want to argue that its a "he said, she said" thing, you're going to need to come to the table with receipts about it, and trump is just completely full of shit on a level that's untenable and weirdly turned into this January thing where we almost had lawmakers killed.