If Trump's presidency was to be ranked now, where would he be?

[Absentee Voting Ghost of Ruin]

I didn't think the subject of a damnatio memoriae got to be on lists.

[Absentee Voting Ghost of Ruin]

Nothing Trump has done yet has quite the same consequences as:

Expelling thousands upon thousands of Native Americans from their land in direct violation of a Supreme Court ruling, condemning many of them to their deaths on the walk to Oklahoma. (Thank you, President Jackson!)
Launching an insane landgrab war to try to steal a third of Mexico under false pretenses and false accusations of Mexican aggression. (Thank you, President Polk!)
Signing the Compromise of 1850, allowing southern slavehunters to drag escaped slaves back south into lifelong bondage and servitude. (Thank you, President Fillmore!)
The Kansas Nebraska Act, abolishing the Missouri Compromise Line and allowing slavery to exist in any territory that wanted it. (Thank you, President Pierce!)
Allowing seven states to secede from the Union with complete inaction and leaving it as a problem for his successor. (Thank you, President Buchanan!)
Trying to undermine Reconstruction and sabotaging Congress' efforts to grant rights to freedmen. (Thank you, President Johnson!)
The sheer scope of felonious and unethical activity the Harding Administration managed to get through in 2 and a half years (Trump's gunning for Harding's record, no doubt).
Inaction and apathy in the face of the gravest and greatest economic disaster in human history. (Herbert Hoover)
Launching an illegal war in Cambodia without Congressional approval or even knowledge that ended up leading to the deaths of literally millions of people. (Thank you, Richard Nixon!)
Illegally running guns to the Iranian revolutionary government to pay for illegally funding Nicaraguan death squads directly counter to Congress. (Thank you, Ronald Reagan!)
Launching a brutal war under false pretenses that destabilizes the Middle East to this day, a war of which we are still dealing with the consequences. (Thank you, George W. Bush!)

Let's keep some perspective here when we say that Trump is the worst, OK?

You literally did not mention the interment of an entire race of people, or the dozens upon dozens of horrible, horrible things Lyndon Johnson did.

I also didn't mention Wounded Knee, Grover Cleveland breaking up the Pullman Strike at gunpoint resulting in dozens of deaths, or the US literally occupying the Dominican Republic for 8 years to force them to spend their budget on paying back their debts to the US at gunpoint. That list could be as long as you want it to be.

My main point was that most of Donald Trump's mistakes haven't killed people yet (yet being the key word), so how could he be at the bottom of the list?

If you count ONLY bad outcomes to date, he wouldn't be. But once you start adding in things like net outcomes (good vs. bad), competence, success at their stated agenda, and probable outcomes of Trump's actions (or those of other recent Presidents) then he rapidly starts to slide to well below the bottom.

[Absentee Voting Ghost of Ruin]

Please....he would be in last.

He can't be behind Buchanan, surely? I mean our country is nowhere near disintegrating.

You could say the same about the US in June 1857. When was when half the country was steaming mad and mortally insulted by a book that said "slavery is bad".

The country today is deeply divided. While the divide isn't only territorial, it has some strong territorial dimensions. With Trump posturing at the helm of our nation, I wouldn't be at all surprised if the US doesn't survive another 8 years.