From some commentaries I read, China has a near 100% chance of winning in war with Taiwan even if US and allies join. This is mostly to do with mainland China's relative proximity to Taiwan and the few relative number of air bases US has on Japan and how far away Hawaii is.
You do know that there is the concept of carrier strike groups which involve you putting a bunch of planes on an aircraft carrier and sailing it to the region. Just like UK's HMS Queen Elizabeth is doing as we speak.
Also there are US air bases in Phillipines, Singapore, South Korea, Australia, Guam etc. This is going to be a regional conflict not just between US and China.
Again. Anyone who says there is a 100% chance of winning is delusional and ignores the history of war on this planet.
China's DF-21/DF-26, assuming they work half as good as they're claiming, will likely largely nullify the advantages of carrier strike groups.
Being able to sink any hostile warship within 2000 miles of the Spratly Islands is a significant deterrent to external military intervention in the region.
Wars are not single battles. If China were to attack (and capture) Taiwan the war would not just be over. The West could attack mainland China and attempt to retake Taiwan.
declarations are pointless, but the US is unlikely to put boots on land in china. The last Korean war, the US decided not to do it (invade into chinese territory), and china was much weaker back then.
To take Taiwan China will need air supremacy as well as naval supremacy lack of either one will make it close to impossible. Think about what it took to do d day possible and that was a much shorter crossing and the combined resources of the allies with full air and naval supremacy.