I think it's much too early to assess the totality of (let me put this in the least inflammatory way that I can think of) Trump's long-term impact. At the very least, he has re-formed the American judiciary, delayed action on climate change by four years, and eroded or eliminated many of the societal and governmental norms that are essential for the functioning of our society (e.g. accepting the results of elections).

But even now, we have North Korea with ICBMs and more nuclear weapons than before, Iran closer to a nuclear weapon than before, and probably a hundred thousand people or so dead from Covid who might not have died if Trump had not politicized the wearing of masks. That's not "little damage" by my reckoning.

There are also a few hundred innocent children who were forcibly separated from their parents and likely will never see them again because of shoddy record-keeping. Despite the relatively small numbers, the sheer monstrousness of this makes it impossible to sweep it under the rug. Trump effectively abandoned the moral high ground that America has held since the end of World War II. America is no longer perceived as a reliable partner, leader of the free world, and beacon of hope. I suppose reasonable people can disagree in their assessment of the long-term impact of this, but in my book, that's not "little damage."

[ADDENDUM] Something else Trump has done is form a significant contingent of the citizenry who now equate the interests of the country with Trump's personal interests, i.e. who believe Trump when he says that we face existential threats that he alone can fix. Ironically, they do this in the name of patriotism and freedom, utterly oblivious to the historical precedents that show time and time again that cults of personality lead to tyranny and ruin. Thankfully, we have not yet crossed that threshold. But we were standing on the brink, and it won't take much to bring us back to it.

[ADDENDUM2] There's also this:

https://slate.com/news-and-politics/2020/11/william-barr-lam...