In the immediate aftermath of the election, two interpretations began circulating about its implications. The first came from conservatives who insisted that America remains a "center right" country and that the voters gave Barack Obama and the Democrats a majority only because of the financial panic and the limitations of the McCain campaign. The second interpretation came from some liberals who promptly declared this to be one of those critical elections that mark a historic political realignment. Neither is the right way to read the returns.

The conservative interpretation ignores long-term trends in demography and public opinion that favor the Democrats. Since the early 1990s, younger voters have been moving in a more liberal direction, and Democrats have solidified their support among Latinos -- the most rapidly growing group in the population. Surveys have shown a steady rise in tolerance on race and sexual orientation as well as large majorities in favor of universal health coverage and other measures requiring an active governmental role. George W. Bush's two victories -- the first only in the Electoral College, the second after September 11 -- may have just temporarily held in check a wave of increasing liberal and Democratic strength.

No doubt economic conditions were crucial to Obama's victory, just as they were to Franklin Roosevelt's in 1932. Every election turns on both immediate and long-run influences. But although the outcome this year was no sure thing, it was also no mere fluke. Democrats gained control of Congress in 2006 before the recession, and they have now won the popular vote in four out of the last five presidential elections.

The claim that America remains a center-right country is an effort to deny a plain fact about the election. Republicans denounced Obama as a liberal, accusing him -- horrors! -- of wanting to redistribute income. Yet after waging an ideological campaign, they deny that the outcome had any ideological significance. So convenient a memory is a marvelous thing.

Nonetheless, the view that 2008 marks a historic realignment in favor of the Democrats is also misleading -- or at least premature. Obama's victory offers no guarantee of a realignment. It is only an opportunity to bring one about.

Some of those who saw a realignment in this year's returns invoked the notion that American history is characterized by roughly a 30-year political cycle, each turn marked by a critical election. As the political scientist David Mayhew has shown, the historical evidence for critical elections is pretty shaky. In 1992, it seemed Bill Clinton's election came right on schedule three decades after the New Frontier and Great Society, but a Democratic realignment didn't materialize, because Clinton was unable to turn his personal victories into a lasting majority for his party.

The potential for a realignment, however, was already growing under Clinton. In 1997, in an article called "An Emerging Democratic Majority" (later the title of a book by John Judis and Ruy Teixeira), I argued that long-term social trends favored the Democrats without guaranteeing them anything and suggested that the Democratic Party itself -- not just the single-issue movements around it -- could become a "cause." Clinton didn't create that cause, but ironically, Bush has. In recent years, for the first time since the 1960s, there has been a movement on the progressive side -- and Obama has brought that movement into the Democratic Party and seems determined to keep it alive.

A genuine realignment will require several things. First, Obama has to get his program through Congress. Second, that program has to show real progress, beginning with economic recovery, in order for Democrats to at least hold their own in 2010 and for Obama to win re-election two years later. And, third, his presidency has to bring about long-term, sustainable institutional change that is understood as a Democratic achievement and serves as the formative struggle of a new political generation.

Of course, the real motive behind claims that this is a center-right country is to suggest that although Obama won a majority, he didn't win a mandate, at least not for the full program he campaigned for. Having lost the election, conservatives want to win the debate over its interpretation and convince the public that the Democrats had better not "overplay" their hand and actually try to change institutions such as health care.

To be sure, the new administration will need to reach out, where possible, to gain support from Republicans and to make strategic choices about the sequencing of reforms. Not everything need be done on day one. But there would be no surer way of wrecking the promise of change than backing off from it without a fight. On Nov. 4, America climbed a mountain, but the ultimate significance of the nation's choice will depend on what's on the other side.