You don't understand. Canadian special forces are so highly trained that they can shoot down incoming missiles, fighter jets, and bombers using bolt action hunting rifles. Those arrogant Americans won't know what hit them. It'll be like Iraq+Afghanistan times 100. Canadians have way more military training, grit, and tenacity than anyone in the world. They can survive off the land by eating snow, and hiding in forests. American satellite constellations cannot monitor them since they've lived among the snow and trees so long that they blend in perfectly.
Canadian service members are more likely to be MAGA maples than not.
The US is playing a game of leverage, here. We saw Trump tell Japan to not escalate the row with Taiwan - but he's been more or less silent on the topic of nuclear weapons. Recently, the US approved South Korea's plan for acquiring nuclear submarines, and on the whole there's a demand from Washington for its allies/vassals to pick up more of the slack on defense related matters. To me, this is a salami slicing tactic to eventually corner China, so that Trump can step in and use it as a bargaining chip either for trade deals or the trilateral nuclear control talks the US has been trying to restart.
Although all efforts should be made to stop Japan, I don't see it as a real problem even if Japan succeed. The Soviet Union and US have both already proven that you can have all the nukes in the world and still get crushed by pure economics, tech war, or trade war. Or be infiltrated and politically divided into oblivion. Likewise, being a nuclear power has not allowed Pakistan to seriously attack India. Nor has it enabled North Korea to seriously attack South Korea.
Right, this is my take as well, I don't see this as an existential defeat for China, because MAD isn't the same as invincibility (unless you're the one without nukes). Between nuclear powers, ironically conventional hard power (military, industrial, etc.) becomes more important in competitive parity. The only thing that is being denied by MAD is total defeat and the ability to inflict it (by either Japan or China).
If that becomes the case, it will raise the requirements for entry into the club (or just to maintain current status of "membership") to a level that even Japan, UK, and France cannot afford. Certainly not at the same time as Japan would be undergoing even China-only sanctions. Just as China and US would never nuke each other over sanctions, nor would Japan do so even if China cuts of all trade ties and uses long-arm jurisdiction to deter and penalize 3rd parties from routing Chinese goods/products containing Chinese inputs. There will still be leaks, but certainly not enough for Japan to maintain their current industrial and societal level. Not even close.
Forget it, The US has to be brain death retarded to leave a nuke in ANY country that they don't have strong military presence and the device is safeguarded by them. Nobody knows if the US and Japan are always going be friendly to each other or if Japan in the future would be friendly to China against US interests, nobody knows that. That is a too high of a risk for any country, to leave a weapon of such caliber behind. No even Israel get that luxury. If Japan want nukes will have to do it the old way, they will have to design a device, test it and deal with all the internal and external backslash that will come with that.