Michael Kazin is co-editor of Dissent and a professor of history at Georgetown University. He is completing a history of the American left to be published in 2011 by Knopf.

Liberals have an obsession with the presidency. Since Franklin D. Roosevelt strode across the political arena like a colossus (albeit a colossus in a wheelchair), liberals have tended to equate success with electing one of their own to the White House. The New Deal, the New Frontier, the Great Society—these are fondly remembered as the glorious, if brief, eras of liberal political history, times when the country seemed to leap forward to a better place, before conservative Republicans found ways to jerk it back again. It's an obsession that also expressed itself in pop culture: After George W. Bush took office, with a big assist from the Supreme Court, many liberals consoled themselves by cheering on Jed Bartlett as he outfoxed his right-wing opponents.

Now that there’s a 50-50 chance that Obama could actually lose, the obsession is saturated with anxiety. Nearly every liberal I know checks the polls every few hours and frets over each debate, as if the future of the republic depends on Obama winning a second term. (OK, I confess—I do it too.) But we should realize that merely electing, or re-electing a progressive president has never been how lasting reform occurs. A one-term Obama administration might be considered a failure—but it would be a failure that liberals would be partly responsible for.

Every chief executive who signed major pieces of liberal legislation benefitted from thinkers, organizers, strategists, and grassroots insurgents who did their most critical work without the aid of an electoral college majority. The Social Security Act culminated over two decades of planning by such brilliant advocates as Louis Brandeis and Frances Perkins—and pressure from a movement of angry old people led by a charismatic physician named Francis Townsend. Only after years of violent mass strikes, including general strikes in San Francisco and Minneapolis in 1934, did Congress pass the National Labor Relations Act. Once workers got federal protection for organizing unions, lawmakers hoped, they would no longer need to pursue that goal by bringing production to a halt....