I’m no space policy expert, (duh?) but I have been thinking along the same lines for a while.
Just giving ISS to the remaining partners, is the best way to end this fiasco.
As to avoiding diplomatic damage caused by withdrawing from our obligations, ...I don’t see any real way around that one. Simberg is right though, having been given the keys to the house, ESA isn’t going to feel terribly put upon. I would be more concerned with Japan and Italy, and hopefully there would be a way to not just smooth things over, but to partner with those two nations even more closely. I expect the Russians would be thrilled, (As long as the EU billions flowed) more so than ESA, but might demagogue the issue of obligations unfulfilled for a while, and that’s alright, because first, they would be correct, and second, that’s just politics.
In the event that relations with Russia and ESA were seriously damaged, and future space cooperation seemed in peril,....ooops! That would just free us to reassess our space exploration partnerships, and form new alliances that might work more strongly in our interest.