Given that a sizeable chunk of the US electorate is wearying of the commitment to Iraq (already), I think the US defense commitment to Taiwan is in serious question.
It seems pretty clear that China is manipulating the North Korean crisis to their advantage. Any move against Taiwan will probably come after a military confrontation on the Korean Penninsula.
I must disagree.
The shock of an attack by China would be enough to get Americans behind a mission there.
In fact, defending Taiwan would be an easier sell than Iraq?
Why? Because Americans aren't too fond of the Chinese; we just get along with them for business purposes. We still recognize their despotic government. Once they attack Taiwan, we would have a clear reason to go in. The whole argument about a preemptive war that occurred before Iraq would not take place then.
How about a deal: Taiwan for North Korea.
We support the non violent transition of Taiwan to the mainland, and China supports non violent regime change in the North and reunification of the Koreas.
I don't think that would work in the real world, but its an idea.