When I first arrived in Taiwan as a college student in the summer of 1973, there was no ambiguity whatsoever about the American role on the island. Over the previous two years, President Richard M. Nixon and his national security adviser, Henry Kissinger, had opened relations with the People’s Republic of China in Beijing. But a short distance away in Taiwan, which the People’s Republic considers a breakaway province, U.S. Air Force jets soared overhead. There was a U.S. base right in Taipei, within walking distance of my favorite bookstore.…