> Ergo the U.S president at that time will leave Taiwan out to dry instead of risking World War 3.

I don't think (or atleast I hope not) the US would use nuclear weapons to defend Taiwan, but I have a hard time believing that the US wouldn't offer atleast token military resistance. At the very least, the US has a lot of standing to lose with it's many allies accross the globe that would make leaving Taiwan out to dry very costly.