At this point, an attack on Taiwan is an attack on the USA. I suspect China is very much aware of this.
The three gorges dam is also hangs a bit of a sword of Damocles for china. A few good hits is as good as a nuke.
The first seems reasonable enough given the proximity to China and Chinese hypersonic missles. The second seems rather fuzzy.
Who or what are you citing? That isn't US policy as far as I know. I can't recall any US president, political party, etc. taking that position.