The fate of Taiwan keeps American policymakers up at night, and it should. A Chinese invasion of the island would confront the United States with one of its gravest foreign policy choices ever. Letting Taiwan fall to Beijing would dent Washington’s credibility and create new challenges for U.S. military forces in Asia. But the benefits of keeping Taiwan free would have to be weighed against the costs of waging the first armed conflict between great powers since 1945. Even if the United States