If this is a shooting war (and blockade of PRC would result in a shooting war), then PRC would deploy area denial assets, which have sufficient range to deny USN operations in the area... Unless USN is ready to take the risks. Which would mean that it would loose a number of surface ships, probably carrier included.
You couldn't just pressure a regional power into doing things by using military force threats and expect no resistance. If pressure is sufficient (ie an all out war with ocupation of Taiwan), then PRC would engage US bases in the region and may shift to tactical nukes.
Morever balance in the region is shifting, at the moment PRC has sort of parity with other regional players (ie Japan and ROK) and something one could count as a possible conventional superiority. This would change over time, as PRC naval build up goes on. If we take the estimates by globalsecurity.org (
http://www.globalsecurity.org/milita...a/plan-mod.htm) then things are not looking rosy for the USN to conduct any meaningfull power projection in there even in near future.
The air/naval bases in that southern area further improve the PRC control of the area, further increasing costs of USN power projection in there.
Note that ROK and Japan strongly dislike each other for historic reasons. India and others are unlikely to commit, unless they were directly hit by PRC first. Hence allies in that war should not be taken for granted.
A war with PRC would also imply the need of Russia to be the Western ally, as otherwise blockade of PRC is not possible.