

You’re never going to get a satisfying answer to this question, because there is no actual reason. If you want, you can go peek in on the conservative subreddits and watch their gold-medal winning mental gymnastics, but the reason Trump is doing this is Putin told him to. The U.S. is destroying themselves for no gain.
There absolutely are Americans who get insulted when you make fun of Trump, you can meet them at any Trump rally. I’d also point out, Trump insulted the PM and the entirety of Canada.