Your fear is that Europe could be conquered, like back in WW2. At wich point the amount of resources the US could spend on Miltiary would go down.
I highly doubt anyone could conquer all of Europe, though individual weaker countries like Estonia is a different story.
Europe is also doing for America:
- working with your Secret Service. Going as far as putting legislation into place that allows your secret sevice to act on our Territory with impunity.
- buying and distributing your products
- taking up the bulk of refugees your armstrade based economy produces.
- cleaning up after your military campaigns, like Afghanistan.
All the things you've listed are things we return in kind in some form or another. Peculiarly in the case of the military, we do a lot for you and you do relatively little for us (with the exclusion of obviously noteworthy allies such as the UK and others who even with their misgivings have stood beside us and always pulled their weight).
Also:
A) Our economy is not armstrade based.
B) Voluntary transactions (wherein you buy a good or service we sell, or vice versa) is not doing something for someone else. It's a transaction, not a favor or anything like that.
C) Many of your countries took part in Afghanistan, even if we initiated it, you are not free to exempt yourselves from it and act like it's all our fault. The dishonesty in this sort of thinking is astounding.
So do not give us that "Europe is doing nothing for US" BS that Trump keeps spouting. The moment you look one second or ask somebody that actually works in foreing affairs, you would realise how wrong you are.
Europe (as a whole) is doing virtually nothing for the USA, and Trump has nothing to do with that. Voluntary transactions are not something you're doing for someone else, you do it for yourself. Or when you rent a hollywood movie are you doing it to support our economy rofl? You doing that means nothing insofar as what you do for us or what we owe each other.