Will Donald Trump become one of the worst Presidents in U.S. history?

[Absentee Voting Ghost of Ruin]

He’s already right there, basically a yuge up. Even the other bad presidents at least were competent and knew what they were doing

[Absentee Voting Ghost of Ruin]

Trump is more inconsequential, then catastrophically bad.

Global Warming and the environment
Enabling abusive big business
Destroying what moral standing the government (and country) had left.
Widening the gulf between factions in American society
He's accelerating destructive trends across the board. The list goes on and on. And it's fractal, too. Trump is encouraging long-term destruction at every level, from planetary to petty.

If he'd just done one massively stupid thing, it might provide the impetus to get rid of him. Instead, he's setting many things in motion (and giving those already in motion a good hard boost) that will bear catastrophic fruit years and years down the line.  Trump isn't working for Putin, he's an agent of Cthulhu.

[Absentee Voting Ghost of Ruin]

Yes.

Future generations will laugh at us for electing him.

The way they laugh at Taft or Harding?  Whose doing any laughing except for the nerds and historians that far down down the road?

No, they won't laugh. (Though there will be jokes.) They will curse. And they will ask, "how could they be so stupid?"

[Absentee Voting Ghost of Ruin]

Trump is incompetent and personally unsuited for the office, but so far at least he hasn’t caused any disasters. He will likely get at least a few good things done over the next three years,

Right now, scribbling his name on a (likely to be hated and condemned) tax reform bill he had nothing to do with and not getting indicted with seem to be the biggest heights he can aspire to.

What do good things (from any political perspective) do you see him likely getting done before he's out of office?

[Absentee Voting Ghost of Ruin]

He will be among the worst.

He'll only inarguably be THE worst if he starts a major war, or causes states to secede, or causes a new revolution, or causes a great depression and a minor war.

He could start a civil war,  or a  domestic insurgency without any states even trying to secede. If there's any one thing Trump can be said to have done, it's encouraging divisions between Americans, and inciting American on American violence.