Taiwan has always expected assistance from the U.S. Navy and Air Force. But without advance warning to get a carrier or two into the area, and a few hundred U.S. Air Force planes alerted for movement to Taiwan, Japan and Guam, the American assistance would be too late. Thus, for Taiwan, an OOTB attack, which the Chinese appear to be preparing to carry out, is something to worry about.
If we can get our power into the fight, we are likely to be able to defeat the Chinese--perhaps decisively. But if the war is over before we react, a free Taiwan is history.