He should just resign now and let Pence be president for a bit.

I'm from the future Biden won.

No point in that then, unless Biden prints up some 46th president signs.

Well, it doesn't look like he's winning....the question is if he'll resign anyways.

Grover Cleveland had to lose to Benjamin Harrison to be both the 22nd and 24th president, but if he wins, Trump could resign from his current term a few days before his inauguration and be the 45th and 47th president. That's like being two presidents.

No reason, just to mix up the order and number of presidents a bit.