Fifty years ago, America was in agony. Its unity at home, and its standing abroad, were deteriorating. Today, the country again faces a profound political crisis, and the summer of 1968 is instructive. One party controls the White House and both chambers of Congress, as was the case then, when Lyndon Johnson was President. But this crisis differs in a fundamental way: fifty years ago, the President’s party had the will to respond. On April 4th, Martin Luther King, Jr., was shot dead in Memphis, and riots erupted in a hundred cities. The next day, Johnson wrote to House Speaker John W. McCormack, a Massachusetts Democrat, imploring Congress to pass the Fair Housing Act, saying, “When the Nation so urgently needs the healing balm of unity, a brutal wound on…