After I retired from Raytheon, I worked as a contractor for the USAF, and interfaced with the Taiwan AF. They devote a lot of their GDP to defense, and pay top dollar for U.S. weapons, and would buy more if we would sell it to them. They pay through the nose for U.S. hardware. There is a limit to what they can do by themselves. The U.S. is reluctant to sell them what could be turned over to the Mainland.
Taiwan has remained independent for seventy years because it is backed by the U.S. Maybe we could get Japan and Australia and New Zealand more involved.
I am not saying we cut them off, just make sure WE are noy paying for it.
Some countries have practically no military at all, because they rely on the USA for their defense.
That is a more likely scenario instead of counting on the U.S. The Taiwanese people are very pro-Japan, and there is already some cooperation between the nations for trade and military drills. It would benefit Taiwan to have the Japanese military defend Taiwan.
The challenge is to enlist the support of the Quadrilateral Dialog in seeing the defense of Taiwan as being in their own security interests. They all know now that China is the common enemy of all of us. For political reasons, the continued independence of Taiwan is of immense importance to the free world.