To name one example, he deregulated the inspection of train safety, despite internal whistleblowers (who were ofc subsequently fired) claiming that the industry was not regulating itself in anything remotely resembling a “safe” manner. Keep in mind, this was before all those famous train derailments happened. Multiple people especially train engineers predicted they would happen, they went to a large amount of trouble - and were fired as a result - of warning that they would happen, but Trump ignored all of that and deregulated the industry to help make it more profitable… and then the derailments happened, whereupon we all paid the price. Socialization of costs, privatization of profits, it is the exact opposite of both socialism and of capitalism both - it was sheer foolishness, period.
And ofc there was his handling of the pandemic - note the initial cause of the pandemic was not his fault, but his poor handling of it is on him. First, at minimum, if nothing else “the buck stops here”. But above & beyond the latter, as the audio recording with Bob Woodsworth revealed, Trump knew that the virus was airborne - he told his friend that much - and yet even knowing that, afterwards he lied and told people that it explicitly was not airborne (again, to aid “the economy”, at the expense of the workers who died as a result). When others, e.g. Bill Clinton, have lied previously, conservatives got angry and tried to impeach them - and rightfully so - so why ignore it when it happens on the other side? Also this lie, measured in the form of “excess deaths”, contributed to the deaths of more Americans than all of our wars combined. That seems like “harm” to me.
Then too there is how he inserted himself between a Congressional decision and the intended recipient of funding, with his attempt to blackmail the Ukrainian government to “just do me a favor though”. By some definitions of the word that might even have constituted “treason” - I am no lawyer though, so be skeptical ofc, especially extreme claims require more extreme evidence, which the first impeachment trial was meant to bring forth except it was halted by Republicans in Congress.
The list really can go on and on… whatever you think of conservative vs. liberal philosophies, or of Republican vs. Democrat politics, he really was quite a dangerous President. Yes, most of us are still alive after his Presidency, but again… many of us are not now, with a good number of those deaths directly traceable to his decisions. Biden may not be “good”, but extremely few Presidents in all of American history come close to how dangerous Trump was, by many objective metrics. History will reveal that, but right now it can be difficult to distinguish b/t the lying liberal media and the lying conservative media sources both lie, for the sake of their own profits. In all of that muddiness of facts, it can be super difficult to find out what is really going on. But the fate of people in and maybe the fate of our actual nation is on the line, so it is worth the effort for those of us who would consider ourselves “leaders” aka citizens, whose votes will determine the course ahead for us all.