To beat Obama, Mitt Romney must channel Rick Santorum

History, we are assured, is written by the winners. But when it comes to American presidential politics, the losers have plenty of say.

Rick Santorum’s exit from the Republican presidential contest this past week cleared the way for Mitt Romney to win the party’s nomination. But over the course of a low-budget campaign that relied almost entirely on volunteers and was met with disdain by the GOP establishment, Santorum won more than 3 million votes and 11 state primaries — the most by a conservative insurgent candidate since Ronald Reagan challenged President Gerald Ford in 1976.

Santorum has been denounced as a sore loser, a religious extremist, a crank. MSNBC host Martin Bashir referred to him as a theocratic version of Stalin. One columnist alleged in the Daily Beast that Santorum would use the power of the presidency to impose “his ideal of a Christian America” on the nation. The New Yorker compared him to Islamic extremists who seek to execute their opponents, adding that we need separation of church and state so that “Santorum and his party can’t impose dominion of one narrow, sectarian, Bible-based idea of the public good.”

But Santorum and his supporters may have the last laugh. From John C. Fremont to William Jennings Bryan in the 19th century to Barry Goldwater, Eugene McCarthy, George McGovern and Ronald Reagan in our time, losing presidential candidates have previewed the ideological trajectory of their parties — and often of the nation.

Romney would be wise to remember this in his general-election campaign. Of course he can’t neglect independents, or women, or Hispanics, or other nontraditional Republican constituencies. But his immediate task is to consolidate conservative support and unify the party. The best way to do that is to appropriate the best parts of Santorum’s message.

Santorum follows the trailblazing evangelical candidates Pat Robertson and Mike Huckabee, who personified the rise and the maturation of social conservatives as a critical component of the Republican coalition.

In the Democratic Party, Howard Dean — his candidacy fueled by fiery online enthusiasm for his antiwar views — signaled the decline of the centrist New Democrats, foreshadowing the emergence four years later of a freshman U.S. senator from Illinois named Barack Obama. Today Obama governs as the most left-of-center president in history, while the Democratic Leadership Council is shuttered.

In the primaries, Santorum outperformed Romney among two key demographic groups, one religious and cultural, the other socioeconomic — and Romney needs both to win in November.

The first group was evangelicals and tea party voters; there is remarkable overlap between them. According to the Faith and Freedom Coalition’s analysis of network exit polls, more than half of voters who cast a ballot in a Republican presidential primary or caucus through mid-March were self-identified evangelicals. In 2008, they made up 23 percent of all voters in the general election. Romney will need them to turn out in even larger numbers to defeat Obama. (He already has a running start; Romney won almost a third of the evangelical vote during the primaries, and a majority of tea party voters in Florida and other critical states.)