Russia, the US and the UK singed a treaty with Ukraine to ensure their borders if they would give up their nukes. Russia is in clear violation of that treaty. How can we expect other countries to sign and respect nonproliferation treaties if we are so willing to throw out whenever Putin decides he wants to gobble up some more territory? If Ukraine had nukes Russia would not be so confident with invading them and if Russia didn't have nukes the US would be so timid about confronting Russia. If nonproliferation treaties are allowed to be treated with such flagrant disregard why would anyone want to sign one or honor one that was already singed? If had signed one and I shared a border with Russia I think I would start spinning some centrifuges.
We probably do not want to get in shooting war over this but we should be putting pressure on our European allies to join us in pressuring Russia to honjor thier treaty. If our allies won't do that then would should just shut down our bases there and tell them they got it.