I think they just fine the entity doing business in the EU. If they don't do business there, I can't see any issues.

I'm not an attorney, but I don't find any cases that extend beyond that.

Quite honestly, it’d be hilarious to see the clown car response from the White House if some EU bureaucrats tried to enforce their GDPR rules on the White House though. “Lol Make us” is the nicest response I can guess at.