Philippines war might be the "safe" bet for US.
Trying to claim parts of China is too dangerous and too ambitious. There has never been a case of a nuclear armed superpower invading another one.
It never made much sense to me that US, which has historically been scared of overtly attacking large and especially well connected countries, would do such a move such as actually using ROC separatists as an excuse to invade China.
But the current Philippines is in no shape to take in China, not even with full US involvement. Not only do they utterly lack weapons and tech, but morale wise, they have no real reason to want war either. It would be a very long term project for US.