Where do you get your 20 year number?
I don't think EU-Chicom cooperation will be developed enough to move on the USA for that long.
There will have to be a few crises where the US is "ordered" by some phony international "laws" to stand down before the populations over there get whipped up enough to pull the trigger - and our armed forces will have to undergo some further deterioration.
But 20 years is a guess - with an Obama administration, it could go much faster. Important to stay proficient.