...or the U.S. intervention in Libya.

Russia's invasion didn't help, but hasn't seemed to trigger major proliferation concerns. In particular, Ukraine has no given any indication of pursuing nuclear development as a result. Indeed, doing so would put their much needed military aid at risk. All indications is that other countries that feel threatened by Russia are making similar calculations.

In contrast, Iran pursuing a nuclear strategy is very much on the table. We've established that their ability for conventional self defense is woefully inadequate; their proxy network has been severely degraded; and their prospect for a diplomatic solution has been repeatedly undermined.

If Iran does get nukes, that could be a catalyst for others in the region to do so as well.