Who? Whoever is trusted by powerful friends to have them, or are powerful enough to otherwise fight those who do, and has serious reason to believe they’ll be needed.
Why? Odds of abuse, or lack of need, equals no nukes for you; responsible & necessary ownership allows. North Korea and Iran are making it very clear they want to kill people with nukes for the he11 of it, so will likely find out the hard way that the Big Boys will disallow it. Saddam’s Iraq was violently overthrown when it looked like he was building nukes, after invading neighbors. Syria gets its nuclear program bombed to smithereens periodically by Israel. India & Pakistan both have nukes, but aren’t going to molest anyone besides each other, which they won’t because of their nuclear standoff. Ukraine found itself a nuclear superpower by accident, and quickly gave them away lest it quickly become a target. Nobody is going to nuke Canada, who relies on the USA to provide such protection in that extremely unlikely case. All of Israel’s neighbors want to obliterate it yesterday, so the USA has quietly furnished nukes as appropriate as deterrent. And the big 3 nuke owners have so many they’re all “f u” to anyone saying they shouldn’t.
Nice summary!
so the USA has quietly furnished nukes as appropriate as deterrent.