It is a European problem. No American blood should be spilled in Europe again.
Then we should never have signed the accession to the treaty assuring Ukraine’s borders and sovereignty. It was okay for you isolationists to remove nukes when it suited you, and now it’s okay for you to betray that country now that such a thing suits you now.
The biggest guarantee for that to be assured would be for Putin to withdraw now immediately, including from Crimea and Donbas area. He can call it a victory, I don’t mind, it would be fine by me.