Strategypage reminds us of what should be obvious:
The U.S. military commander in the Pacific pointed out that American operations in Iraq and Afghanistan have no practical effect on the U.S. ability to defend Taiwan. For that, warplanes and warships are needed. Few of these are engaged in the Iraq and Afghanistan fighting, and are available for any operations around Taiwan.
We have many different types of power. Our Army and Marines can't keep up the current pace for long but the Navy and Air Force are tanned, rested, and ready to work.