Taiwan is no part of NATOIf China attacks first, then yes. If the US doesn't even defend Taiwan in face of a Chinese attack, how would its other allies expect it to do so? NATO would collapse if this was the case ...
https://www.newyorker.com/magazine/...urds-and-trumps-abandonment-of-foreign-policy
https://www.wsj.com/articles/u-s-de...or-ukraine-but-doesnt-promise-arms-1503586126
https://edition.cnn.com/2016/10/31/...-scarborough-shoal-south-china-sea/index.html
How many times US defense pact or allies collapse given US had given broken promise and failed to defend allies on so many occasion?
US dont even have will to defend themselves or strike back Iran when their military base in Iraq is directly attack by Iran with ballistic missile? And now you claim US will defend Taiwan. LOL.
US in the eyes of allies is an unreliable partner. Those pact signed are just a formalty with no real meaning. It will depend on the enemy face first. If the enemy is small fried which can be easily taken care with. Yes, US will attack.
NOw you are talking about China size and military. American are not stupid. They know who to pick their enemy to fight in real war.