There are very good reasons why, until Trump, Nixon was the only chief executive to have associated himself with such a strategy: It makes no sense for a confident, great power. Since Pearl Harbor, the United States has acted as a leading partner in grand alliances designed to defeat vicious adversaries and then maintain some semblance of international peace. Such alliances—whether the Big Three of World War II or the postwar North Atlantic Treaty Organization—are founded on trust that, to put it bluntly, you would take a bullet for the other guy. These don’t work as well if the states at the helm, as personified by their leaders, are erratic or irrational. You cannot be both a reckless madman and a reliable alliance partner. Throughout the Cold War, for example, the U.S. worked hard to encourage non-nuclear allies like West Germany to accept “extended deterrence,” the idea that they did not need their own nukes because the United States could be relied upon to defend them. Nonproliferation, which is difficult in the best of times, becomes impossible if the foreign ally thinks the American president is erratic and untrustworthy. It is inconceivable that John F. Kennedy, Gerald Ford, or George H. W. Bush, for example, would have believed it useful for any foreign leader to think him “crazy.”…

There can be little debate, however, over what Nixon’s calculated unpredictability abroad achieved at home. It tore this country apart. In a declassified “eyes only” memorandum to Alexander Haig on May 20, 1972, after ordering the mining of Haiphong harbor, Nixon explained who his domestic audience was: “The hawks are our hard core and we must do everything that we can to keep them from jumping ship [in reaction to arms-control talks with Moscow] after getting their enthusiasm restored as a result of our mining operation in the North.” The madman approach was not just for Hanoi. Nixon wanted his base to know he was tough, thus distracting attention from his simultaneous efforts to build bridges to Hanoi’s communist patrons in the Kremlin and the Forbidden City.