Us, never. Just like with China you can’t win a land war over here, and a home attack has a greater risk of uniting is against a common enemy.
Taiwan possibly. Though I don’t think so. Taiwan is much more useful as a political chess piece that China can beat their chests about. They can invoke the island and be offended about support for it whenever they need leverage right now.
Not to mention it isn’t just the US alone that needs Taiwan and movement there risks a global response.
Define support.
They’re not devoid of allies beyond the US and in general have vocal support of most of the western world.
But only 13 countries recognize them as a country, but not even the US is on that list of 13. Interestingly however, the Vatican does recognize them.
Which is why, they’re remain a nice political chess price for China.