If Republicans don’t want to consign themselves to irrelevance, they’d serve themselves well to look back to that most maligned of decades, the 1970s. In the years of Jimmy Carter the Republicans were similarly divided, but they recovered and even flourished.

By 1977, after the triple blows to the American psyche of Vietnam, Watergate and an economic crisis that lingered into the 1980s, the Republicans appeared hopelessly divided. Internecine warfare threatened to tear the party apart. This division ran the risk of continuing indefinitely the Democratic ascendancy that began with Franklin Delano Roosevelt’s New Deal coalition and re-establishing liberalism’s place as the defining paradigm in American politics.

By 1976 Gerald Ford, a member of his party’s moderate wing, found himself virtually besieged by the GOP right wing. No critic was more vocal than Ronald Reagan, the former California governor with an amiable fa e but a deadly serious sense of politics. Many people, including such arch-conservatives as Dick Cheney and Donald Rumsfeld, who by the end of the Ford years served as presidential chief of staff and secretary of defense respectively, undermined Ford from within the administration.

But a series of funny things happened on the way to the Democratic stranglehold on American politics. Bad luck and dubious leadership during the Carter years and the seemingly innate Democratic tendency to snatch defeat from the jaws of victory undercut the party. More important, though, was the continued rise of Ronald Reagan. By 1981 the Democrats, not the Republicans, were on the ropes, and Reagan stood at the beginning of two terms so vital they made the years from 1980 through 2008 “The Age of Reagan.”

Given this history, and the particularly rapid turnaround from Republican desperation to Republican preeminence 30 years ago, today’s GOP need not despair, and Democrats ought not to celebrate. Four years is a generation in American politics and a lifetime in political memories. But the lesson from the 1970s rings clear. It is fine for the Republicans to embrace conservatism. But in so doing they should not reject moderation.

Consider the state of American politics in the waning weeks of 2009. The euphoria of Barack Obama’s election a year ago and his inauguration in January is long gone. He’s rolled the dice on an ambitious but treacherous health care agenda whose passage is far from certain. He operates within a poisonous climate of personal attacks and vituperation that gains steam in the maelstrom of a 24-hour news cycle.

Republican desperation to regain power and determination to see Obama fail further exacerbate the situation. Obama could well end up enjoying a fine presidency. But success is far from guaranteed. In November 1977, after all, Jimmy Carter still had hopes for a successful presidency. Look how that turned out.

But if Republicans can find succor in history, they cannot hinge all of their hopes on a repetition of their experiences during the Carter years. For on the horizon in the late 1970s was Ronald Reagan. One of the most transformative figures — for good or for ill — ever to take on the presidency, Reagan mobilized the right. But mobilization requires leadership, and the Republicans have few serious leaders in sight.

In 1977 Reagan represented the GOP’s disenchanted, angry and ambitious right flank. In November 2009 that angry fragment of the party is embodied by Sarah Palin, Michele Bachmann, Joe Wilson and their ilk. These politicians have mobilized the Tea Partiers with their Glen Beck-fueled inchoate rage, the Town Hall screechers with their spittle-flecked vitriol and “death panel” talking points, the denialist “Birthers” with their tenuous grip on reality.

These populists have no sense of how to unite their party around them. They have revealed no toleration for the Big Tent of Republicanism that allowed Ronald Reagan to attract disenchanted “Reagan Democrats” while still steering the party and country rightward. They have shown no inclination toward the kind of compromise that characterized President Reagan on issues ranging from taxes to negotiating with the Soviet Union.

For all of his conservative bona fides, as far back as his 1966 California gubernatorial campaign Ronald Reagan declared his 11th Commandment, “Thou shalt not speak ill of any fellow Republican.” Reagan was the central figure in a conservative insurgency, but he knew that he could not destroy his party in order to rebuild it; that change had to come from within. The result was the Age of Reagan.

The question is whether today’s conservative Republicans understand that they cannot save their party by destroying it. Too many on the right have tried to conciliate a base that craves ideological purity. But ideological purity does not lead to victory. It leads to irrelevance.