Donald Trump is a de-facto incumbent US President ("Why I think Joe Biden decided to run again (and why he can’t really talk about it)")

This is a straightforward idea and seems correct. Anyone besides Biden who runs against Trump will be running against the incumbent and be at a huge disadvantage. It doesn't matter that Trump is not actually the incumbent, and should not be eligible, and would not get very many votes if the media did a proper job and if people weren't so easily swayed by propaganda.

This makes sense, and could be enough in the absence of strong leadership. That being said they could put in a literal sock puppet and I'd put my vote in just to negate the alternative, and that's where hopefully most of us are at at this point.