Unless Trump wants to start WW3 the US won't be able to do anything, and even if he did start WW3, Europe would be able to destroy those bases.
The whole point of them was to give the US influence while improving US security. Given Europe can't trust Trump will come to their aid, they won't give the US as much influence over Europe.
Have you ever wondered why the US is able to spend so much on its military? Ever wondered why the US keeps on printing the dollar that's not backed by any gold reserve and other nations still give you real things such as food, resources, goods in exchange for it?
Here's a hint! It's your military. To put it bluntly, European nations and other US allies pretend the dollar has actual value and the US in turn guarantees security and backs the world order based on the rule of law.
Looks like the US is looking to pull out of its end of the deal. That's fair enough, being the world's policeman is sure a heavy burden to carry. I just don't see many people recognizing the implications for the US economy.
The whole point of them was to give the US influence while improving US security. Given Europe can't trust Trump will come to their aid, they won't give the US as much influence over Europe.