Nothing is stopping them from leaving the treaty. If it means your survival, it is a no brainer. Depending on other nations to honor their agreements for protection, etc is a joke. You have the US President openly speaking about annexing other nations and joining hands with Russia, Iran and North Korea. If that isn't enough of a warning than I don't know what is.

> can't just up and start assembling nukes in a basement without effectively dismantling the entire non-proliferation framework

Genuinely curious: what reason do you see they have to avoid this dismantling?

The fact that it's been reasonably (if imperfectly) effective for a very long time and statistically speaking, nobody is really looking forward to a universe in which, say, border or trade disputes turn into nuclear brinkmanship and the risk of proliferation to non-state actors is greatly increased. These agreements exist and continue to exist because the parties find them beneficial. I don't think a bit of ill-conceived smack talk from a Polish PM changes that.

I mean, Israel, South Africa, India and Pakistan did it, and the world didn’t end.

The NPT is arguably a relic of a world in which NATO was considered reliable. We may not be in that world anymore. If Putin invades Poland, will the US help? Or will Putin wave the piss tape in Trump’s face and bring him to heel? This is not as clear-cut as one might like it to be.

I didn't say anything about the world ending and none of these countries were NPT signatories. South Africa joined eventually.