[William Tell]

Non-Sequitur said: "And what clause of the Constitution do you base that on?"

Oops. Can I have a do-over?

The Twentieth Amendment appears to address the issue: " [...], or if the President elect shall have failed to qualify, then the Vice President elect shall act as President until a President shall have qualified; "

So, Biden it is.

[El Gato]

So, Biden it is.

But only until a President shall have qualified. Not permanently as is the case when a legitimate President is removed or dies.