In Germany, he would get crushed and destroyed. Perhaps 15-20%, probably even less. I really have to agree with what has been written by my fellow posters: It's hard to overstate how deeply unpopular Trump is in large parts of Europe. I know die-hard conservatives and self-declared reactionaries and even these people despise him for lacking political acumen and intellectual refinement; I guess that he would only perform well with certain segments of the far-right and perhaps with some protest voters. Concerning the EU: Barring one or two countries in Eastern Europe, I don't see him winning anywhere to be honest. Safe Biden.
I think it would actually be something like 89-11% in Germany in a binary choice. There is almost nobody here who likes this guy. A recent poll found Biden leading 86-6% as preferred US president. Trump not even gets all AfD supporters.
Very well possible and would not surprise me in the slightest. Would still be curious for Friedrichshain-Kreuzberg results in such a scenario. Below 2%?