I don't think great man theory has anything to do with this. US is becoming isolationist because the material conditions are declining, and a large chunk of the populace is now seeing the empire as a drain on them. That's what's making the isolationist rhetoric popular. Meanwhile, nationalist governments that get in power in Europe will almost certainly start doing trade with Russia and China again. We are already seeing this with Hungary right now. It's basically the only way to stabilize their economies, and US has absolutely nothing to offer there.

Aside from radlibs, most Europeans don't actually see Russia as their main problem. They might not like Russians, but they're not interested in a war with Russia, and they don't want to make further sacrifices in their standard of living. At the end of the day, it all comes down to material conditions.