The Hubert Humphrey of 1948 already sported the widow’s peak that would become pronounced later in life; he had the Sunday-school earnestness of a Midwestern druggist—which he was—and the unquenchable zeal of a reformer. In Minnesota, he had driven the Communist-influenced left from the state’s Democratic-Farmer-Labor party. In 1947 he had helped found Americans for Democratic Action, the leading organ of the anti-Communist left. Humphrey and his ADA colleagues worried deeply about the appeal of Henry Wallace, the third-party candidate who opposed the Cold War and endorsed European-style socialism. Idealists were shearing off from the Democrats to Wallace. A bold civil-rights plank in the Democratic platform would go a long way to blunting Wallace’s appeal.

President Truman had appointed a Civil Rights Committee whose final report, To Secure These Rights, had called for federal anti-lynching laws, the prohibition of the poll tax, the desegregation of the armed forces. But the party depended on the “solid South,” and the Southern barons, led by Senator Strom Thurmond of South Carolina, balked at anything that would allow the federal government to preempt state law. Truman had thus endorsed an innocuous civil-rights plank. Humphrey and the ADA had only reluctantly brought themselves to support Truman—and now Truman was abandoning his own principles.

Humphrey wangled a spot for himself on the platform drafting committee, where he fought for a civil-rights plank that reflected the findings of To Secure These Rights. “The party elders,” he recalled in his memoirs, “argued that we were going to split the party by causing a Southern walkout.” Democratic Senate leader Scott Lucas of Illinois called Humphrey a “pipsqueak,” and accused him of wrecking the party. In his diary, Truman referred to the civil-rights plank as “the crackpot amendment.”

The Humphrey plank was easily defeated in committee. The party’s entire hierarchy, and not just the Southern racists, opposed it. Humphrey knew that he had to be a good team player or risk his brilliant future. Nevertheless, he concluded, “for me personally, and for the party, the time had come to suffer whatever the consequences.” He agreed to bring up the measure before the full convention. ADA members fanned out into the hall to buttonhole delegates. Humphrey approached Ed Flynn, the fearsome boss of Tammany Hall; and Flynn, incredibly, said, “We should have done this a long time ago. We’ve got to do it.” Flynn had not suddenly turned Lutheran moralist: He knew that the party couldn’t afford to lose black and Jewish voters to Wallace. He promised to bring in Frank Hague, the boss of New Jersey, and the other big-city wheelhorses. The tide in the hall began to turn.

Humphrey was the Joe Biden of his day—irrepressible, unscripted, prolix. But as he prepared to deliver a speech introducing the minority civil-rights plank on the night of July 14, a speech that he knew would be the greatest political moment of his life to date, he wrote out his remarks, and he kept them short. Sixty million Americans followed the proceedings on the radio, and 10 million more watched on the new medium of television. (The audio version survives, but not, apparently, the video.) “There can be no hedging,” Humphrey cried in his eight-minute address, “no watering down. To those who say that we are rushing the issue of civil rights—I say to them, we are 172 years late.” The cheering of thousands of delegates became a sustained roar. “To those who say this bill is an infringement of states’ rights, I say this—the time has arrived in America. The time has arrived for the Democratic Party to get out of the shadows of states’ rights and walk forthrightly into the bright sunshine of human rights. People—people—human beings—this is the issue of the 20th century.”