This. It doesn't make sense to talk about how hard China will respond to an use of nuclear weapons - tactical or otherwise - by the US, because the US has escalation dominance, meaning it gets to decide when escalation happens, NOT China.The problem is that China currently doesn't have enough nukes to ensure the annihilation of CONUS. Should be sprinting to parity ASAP.
As long as that's the case, the US can do whatever it wants. US elites have never been shy about sacrificing their own for foreign policy goals. Not to mention they can get on a plane to Europe even if the entirety of North America becomes a nuclear waste land. From the perspective of white European elites who travel the Atlantic on a regular basis, the New World is an adopted home land, not the original.
China doesn't have that sort of escalation dominance, because 1) it doesn't have enough weapons and 2) it doesn't control enough territory as the great Western colonial empire. Only the first of these is under China's control, so a nuclear arms race is inevitable.