I stand corrected: we don't have a treaty as such, not since the formal recognition of the Communist Chinese Government in the late '70s.
What we have instead is the Taiwan Relations Act and other subsequent legislation which provides us the cover to supply Taiwan with defensive armaments and kind of weasel-words around whether we'd join the fight if they were attacked.
The idea that the US would step in is the only thing that has kept Taiwan out of Chinese Communist hands all these years.
Sorry, I have desire to pay for defending Taiwan. We already do business with Red China, so I’m not really seeing what the difference would be for me if Taiwan was also Red China.