Has China changed posture, or has the requirement for deterrence increased?It was only under Xi that China changed from a posture of minimum/limited deterrence to pursuing parity
The bigger China is, the bigger the payoff for the US in doing a first strike. A handful might be enough to deter adventurism in the DPRK, or China a few decades ago, but for China now, the US might well decide that taking out its biggest rival is worth losing a few cities over.