President Trump should send the deputy secretary of state to Taiwan and a Virginia-class submarine through the Taiwan Strait.
But why send a submarine instead of a carrier strike group?
Answer: credible, realist deterrence.
For one, were the U.S. to send a carrier through the Taiwan Strait it would infuriate China and risk a major escalation in other areas such as the South China Sea. But it would also be a transparent form of U.S. blustering. After all, the U.S. knows that China knows that even if the U.S. became involved in a conflict over Taiwan, the U.S. Navy would position its carrier groups well away from the Taiwan Strait.
Doing otherwise wouldn't only risk the loss of 6,000 U.S. personnel at the hands of Beijing's carrier-killing missiles and saturated coastal forces, it would do so for no real gain. Aircraft carriers are designed to deliver air power against an enemy, but even the air wings of three carriers would be overwhelmed by the Chinese air force so close to Chinese territory. The costs of such an engagement would thus be far higher than the tactical benefits. At the same time the U.S. would be unlikely to strike the Chinese mainland in prudence against sparking a major escalation to the conflict.
The utility of the U.S. Navy's Virginia-class attack submarines is a wholly different matter.
Because China also knows that Indo-Pacific Command's Virginia-class submarines could cause major problems during an invasion. Those submarines and their crews fundamentally outclass their Chinese submarine counterparts and destroyers. Their complement also includes the USS Illinois, which was recently upgraded with advanced sensors and a land strike capability. This means, as the commander of Pacific submarine forces explains, that the U.S. can "penetrate adversary defensive perimeters ... deliver attacks with surprise at a time and place of our choosing ... and be survivable."
But how would these forces be employed in any conflict?
Well, seeing as Taiwan is just over 100 miles from the Chinese mainland, operations in the very shallow Taiwan Strait would compress U.S. submarines in vulnerability to China's land-based missile forces, as well as naval and air power. For those reasons U.S. submarines would likely be kept in the deeper waters south and to the northeast of the Taiwan Strait. There they could harass Chinese naval reinforcements coming from Chinese bases to the north and south. U.S. destroyers, cruisers, and carriers could support the submarine bubbles and Taiwan's replenishment by operating at distances beyond Chinese power projection reach. The Chinese military would be very reluctant to contest these U.S. assets far out at sea because that would allow the U.S. to bring its overmatch capabilities to bear. Finally, as Defense Secretary Jim Mattis corrects the Obama administration's stand-off missile slumber the U.S. will also soon be able to join these operations with long-range missile strikes. My map below (arrows=missiles, circles=submarines, squares=carriers, etc.) offers a basic example of how these operations might be conducted.
There are some major caveats here. Most obviously, it remains necessarily questionable whether U.S. involvement in a conflict over Taiwan would be in our critical national interest. Japan and the Philippines might also refuse to allow the U.S. to station missiles on their soil. And Taiwan continues to spend too little on defense and steal too many U.S. secrets.
The best outcome is one in which China reduces its threats to Taiwan in recognition of the risks of doing otherwise. At that point we can restore a more peaceful status quo of stability.