This question is probably worth revisiting after 2024's election, since Trump may still have more mileage. A second term might be more dangerous than the first was. Assuming he doesn't win, then his legacy will mostly be all of the weird and slightly hard to measure changes to American culture, specifically conservative political culture.
He generally seems to have made more dangerous ideas popular but also to have made getting a governing coalition together to actually enact those ideas more difficult by eroding the Republican party. Bush's foreign policy decisions seem to have been far more dangerous so I think I'd vote for Bush being the worst as of right now.
That said, Trump still has a non-zero chance of bringing real American fascism into power so that would change things.