Commentary President Donald Trump has plenty to do before the Inauguration. But even now, he can take a single simple step that will add crucially to U.S. security. Half a century ago, the United States adopted a policy that wound up gravely diminishing American power. At the time, it seemed like a good idea. The United States was locked in a deadly rivalry with the Soviet Union. As a way out of his Soviet dilemma, President Richard Nixon chose to take a backward behemoth and elevate it to great-power status. When Nixon sent his adviser Henry Kissinger on a surprise visit to mainland China in July 1971, he extended de facto recognition to the People’s Republic. As a diplomatic gesture, the move gained universal success. For the first time and not the last, monolithic communism appeared as a paper tiger. The U.S.–Soviet conflict was suddenly far less ominous. Nixon and …