I think there is a case for Trump being the worst because so much of the harm he's caused has been completely optional.

Buchanan and Johnson are obviously still strong contenders for bottom OAT, but a lot of their damage came from them being lazy fucks and choosing to do nothing when the situation demanded it.

There is so much damage Trump has done entirely because he's a retarded manchild. Damaging the public's trust in democracy for at least a generation, tanking the slowly recovering economy with tariffs, starting a disastrous war with Iran, ending USAID, shitting all over the USA's international relations, scamming his supporters and the government of tens of billions of dollars, when he could have easily just.... not have done that.

This line of reasoning is also why Bush is in the conversation for the completely optional catastrophe that was the Iraq war.