Let’s say Trump wins and Europe loses its security guarantee from the US.
Then the EU beefs up its military and coordinate its combined forces and military production up to the point that they are no longer in need of US military assistance in future conflicts.
What will be the ramifications for the US if this was to play out in terms of trade, geo political influence etc.
So, the USA has been trying to pull out of Europe for a while from a military standpoint. The EU is large and rich enough that it should be able to protect its own frontier without American involvement. It just happens to be that Europe would rather have the USA pay for its security rather than do it itself. So the EU is going to have to figure out creating a military and all that comes with it; effectively making the EU a nation.
If the USA leaves Europe, it will likely leave the Middle East as well. Oil isn’t worth controlling any more and the USA doesn’t have any interests there besides Israel. I expect more wars in the region as nations realign to more stable borders. This will likely include a lot of genocide.
I expect the USA to focus on the Americas, maintaining an anti-Chinese coalition, and trying to slow dedollarization. Asian allies will likely tolerate a fascist America more than Europe would.