The Democrats' victory -- and Barack Obama's -- was overdetermined and underdelivered.

Overdetermined: Huge majorities believe the country is on the wrong track and disapprove of George W. Bush; voters prefer generic Democrats over Republicans by 10 percent or more. But Obama beat John McCain by (at this writing) just 52 to 46 percent, running 2 points ahead of Bush in 2004 and 1 point behind George H.W. Bush in 1988. Democrats fell short of the 60 votes they need to stop filibusters in the Senate and made more modest gains in the House than the leading prognosticators expected.

To be sure, Obama ran a skillful campaign. Just as he capitalized on Hillary Clinton's weakness in party caucuses (she won more votes and delegates than he did in primaries), so in the general election he used his unprecedented ability to raise money by breaking his promise to take federal funds and by disabling the address verification system that would have screened out many illegal credit card contributions.

Such actions by a Republican, as Washington Post media critic Howard Kurtz has argued, would have gotten scathing coverage from mainstream media. Not so for Obama. His campaign outspent McCain's vastly on ads and organization in target states. That probably switched 1 percent or 2 percent of the vote in five key states -- Florida, North Carolina, Virginia, Ohio and Indiana -- which meant that Obama won a solid 364 electoral votes rather than a Bush-like thin majority of 278. All of which shows a certain ruthlessness. But ruthlessness is a useful quality for a president (see Roosevelt, Franklin; Reagan, Ronald).

Do Obama and the Democrats have a mandate? Obama got a larger percentage than any other Democrat since 1964, and Democrats have congressional majorities comparable to those in Bill Clinton's first two years. But their policies of protectionism and greater taxes on high earners seem ill-suited to a country facing a recession (see Hoover, Herbert). The public fisc does not appear to be overflowing enough to finance refundable tax credits, government health insurance or universal pre-kindergarten.

The half of the electorate that doesn't remember the 1970s may be more open to big government than those of us who do. But "open to" does not equal "demand." The decisive shift of public opinion came when the financial crisis hit. McCain approached it like a fighter pilot, denouncing Wall Street, suspending his campaign, threatening to skip the first debate. Obama approached it like a law professor, cool and detached. Voters preferred law professor to fighter pilot. This was a triumph of temperament, not policy.

Are we seeing a political realignment? Certainly some of the ingredients are there. As presidents, Reagan and Clinton attracted young voters to their parties; G.W. Bush signally failed to do so. Obama, before he has started governing, has inspired fervent, even quasi-religious devotion from the young and has brought millions of them into the electorate.

Judging from the polls and from my first look at the election returns, I believe he has attracted to his party many affluent, highly educated voters in metro areas running south from Philadelphia to Charlotte, N.C., and Tampa, Fla., and west to Denver and the Pacific. Democrats directed much rhetoric toward the white working class, but failed to win most of its votes. Instead, they assembled what you might call a top-and-bottom coalition: affluent suburbs plus blacks in central cities.

The Democrats have always been a party of unlikely coalitions, capable of expansion when their leaders perform well, susceptible to disarray when they falter. The roughhewn John Murtha helps bring the designer-dressed Nancy Pelosi to power; the African-American quasi-academic Obama inspires millions in the highest- and lowest-income ZIP codes. And, as McCain handsomely acknowledged, there is something genuinely thrilling in the spectacle of Americans electing a black president.

But presidents can build majority coalitions only through performance (see Bush, G.W.). As president, Obama faces daunting problems. How to fix a financial system no one seems to fully understand. How to defeat terrorist enemies sheltered in the territory of our putative ally Pakistan. How to live up to the high expectations so visible in the cheering and tearful faces in those crowds in Berlin, Invesco Field and Grant Park -- after a victory that was thrilling, but not quite what the Democrats hoped for.