it would be his stance on war (him being against it and try to pull out of them). Though, I have much less knowledge or actual influence on such matter so I can take a much simplistic approach as to I am against it. But as the leader of the country, there are more on the line than simply against it. It has to be done more thoroughly and follow in line with our country's previous and future stance. I do think Trump has weakened the US in the world stage due to some of his stance on the issue.
I think you also forget the impact that Trump have on the country. We were always divided as a country but the divide has widen a whole lot under Trump. I used to be able to argue and agree on some stuff with republicans. Actually, I used to think I lean right (on fiscal issue) more than the left. But now, I can't seem to talk to any of them anymore. Trump made "saying the quiet part out" normal for republicans and they don't think they are wrong for it. It makes any conversations with them extremely difficult. The implicit racism, sexism, etc are imbedded in everything they say now. Trump also made the conspiracy theory fraction in the republican party mainstream. We have our conspiracies on our side but our party leader are mostly very good at keeping away with those CT. Thus, not making them mainstream. To be honest, I think the divide deepened as Trump left office.
So domestically, I think Trump is a way worst president for the country. Trump's only saving grace was that he didn't start a war.