I think launching a war of distraction, or the threat of dropping nukes has been removed. That was a big worry IMO. This is no take-backsies fudgery which seems to have been avoided thankfully.
The pardon fudgery past and future, which although is a misuse of presidential power and galling to anyone who believes in justice, is a lesser evil and will play out in the courts over the coming year, especially if he tries to pardon himself.
The rush of toxic environmental rollbacks he has been engaged in will be undone. The infamous Keystone pipeline will be nixed on day one. Anything pushed through by Trump in the last 60 days can be nullified overnight with the stroke of a pen (using the Congressional Review Act). One lesson learned by the incoming Biden admin is that flooding the zone works. There will be a deluge of EO's in the first few days - too much for the media to keep up with - in true Trumpian fashion.
Some stuff can be dealt with quickly but the longer-lasting fallout of this presidency will be the division of America itself. The rise of qanon and white power terrorism is not something easily remedied.