Ukraine

Letting Ukraine into NATO is actually still a way to prevent Ukraine from getting nukes. That's been an undercurrent for this whole war. Ukraine is a near-nuclear state. They were the Soviet rust belt. Ukrainians were fully involved with the Soviet weapons development, and there are still people alive in Ukraine today who worked on those bombs and know how to make them. Hell, they probably still have a lot of the old drawings and technical documentation lying around somewhere. Ukraine also operates several power and research reactors and would have no problem getting its hands on some plutonium. Realistically they could have a bomb in just a few months if they wanted to badly enough.