I reject the premise of this question. Let's stop pretending there were 45 presidents.
That being said, at this point, Trump's incompetence has limited the amount of damage he's been able to accomplish, so at this point, there's still a few Presidents below him. I'd say Polk, Buchanan, Johnson, Nixon, Reagan, and Bush II are still below him, in no particular order.
Uhm...
I was referring to Andrew Johnson, not LBJ. I'm guessing I don't need to justify that one.
With regards to Polk, if I'm going to rate Buchanan as harshly as I do, it would take quite a bit of cognitive dissonance to not judge Polk similarly.
While there's no one, damning thing I can point to with Reagan, like, say, the Bush and Iraq or Buchanan and slavery, I think in sheer number of individual horrible things done while in office, the Reagan administration has to take the cake. From his support for death squads, terrorists, and dictatorships abroad, to his policy of "Reaganomics" at home, which created a great deal of misery by leading to things such as dramatically increasing homeless, environmental destruction, union busting, to his Jim Crow-esque drug policies, to the fact that he was literally a traitor, Reagan definitely warrants a mention when discussing the worst presidents. And I won't even say anything about the AIDS crisis, because Reagan didn't either.
