"About four-in-ten Americans (38%) approve of Trump’s job performance"
I assume that is well below the percentage of Americans that call themselves Republican. Not fully understanding your point. The language in your link seems to confirm it's a serious issue for Trump.
That depends entirely on the votes that happen this year. The point is, those republicans aren't going to risk losing almost all their guaranteed votes that come from republican voters.
https://www.pewresearch.org/fact-tank/2020/08/24/trumps-appr...
Also see: The most recent RNC.