Robert Dallek, finalist for the 2008 Pulitzer Prize for Nixon and Kissinger: Partners in Power (HarperCollins 2007) and winner of the 1979 Bancroft Prize for Franklin D. Roosevelt and American Foreign Policy, 1932–1945 (Oxford University Press 1980), is a professor of history at Stanford University.

In 1965, after winning in a landslide against Barry Goldwater and helping to carry Democratic supermajorities into both houses of Congress, President Lyndon Johnson set out to enact a battery of Great Society reforms, including Medicare, government insurance for seniors. Despite his political mandate, 60 years of conservative opposition to such a measure meant proceeding with caution. Later, California Governor Ronald Reagan, for example, would characterize the Medicare bill as the advance wave of a socialism that would “invade every area of freedom in this country.” Reagan predicted that this reform would compel Americans to spend their “sunset years telling our children and our grandchildren what it was like in America when men were free.”

With 63 percent of Americans favoring passage of Medicare, Johnson believed that diehard conservative Democrats such as Wilbur Mills, the chairman of the House Ways and Means Committee, who had repeatedly blocked a Medicare bill from reaching the House floor, would be hard-pressed to maintain his opposition. Johnson had little leverage over Mills, who had a safe seat and feared that Medicare would bring fiscal disaster upon the country. Privately, Johnson complained that Mills was a “prissy, prim, and proper man . . . [who] was afraid to put his reputation behind a risky bill.”...