Ronald Reagan famously quipped that the Democratic Party left him before he left the party. Like many progressive supporters of Barack Obama, I'm beginning to have the same feeling about this president.

Consider what we've seen since the shellacking Democrats took in the fall elections.

On Afghanistan, the administration has intimated that the 2011 pullout date is "inoperable," with the White House talking 2014 and Gen. David H. Petraeus suggesting decades of occupation. On bipartisanship, the president seems to think that cooperation requires self-abasement. He apologized to the obstructionist Republican leadership for not reaching out, a gesture reciprocated with another poke in the eye. He chose to meet with the hyper-partisan Chamber of Commerce after it ran one of the most dishonest independent campaigns in memory. He appears to be courting Roger Altman, a former investment banker, for his economic team, leavening the Goldman Sachs flavor of his administration with a salty Lehman Brothers veteran.

On the economy, the president has abandoned what Americans are focused on - jobs - to embrace what the Beltway elites care about - deficits. His freeze of federal workers' pay, of more symbolic than deficit-reducing value, only reinforced right-wing tripe: that federal employees are overpaid; that overspending is our problem, as opposed to inane tax cuts for the top end; that we should impose austerity now, instead of working to get the economy going.

Now the not-so-subtle retreats are turning into a rout. The president is touting a NAFTA-like corporate trade deal with South Korea. He appears to be headed toward supporting cuts in Social Security and Medicare and irresponsible reductions in domestic investment. And he's on the verge of kowtowing to Republican bluster and cutting a deal to extend George W. Bush's tax cuts for the rich in exchange (one hopes) for extending unemployment insurance and possibly getting a vote on the New START treaty.

This is political self-immolation. Blue-collar workers abandoned Democrats in large numbers in the fall; wait until they learn what the trade deal means for them. Seniors went south, probably because of Republican lies about cuts in Medicare; wait until anyone over 40 who's lost their savings hears about Alan Simpson's plan to take it to the "greedy geezers." The $60 billion each year in Bush tax cuts for the richest Americans could pay for universal preschool for America's children, or tuition and board for half of America's college students.

The stakes are much higher than the distant election. The president has suggested unconvincingly that he'd prefer to be a successful one-term president than a two-term president who didn't get anything done. But there are other alternatives. If the president continues on his current course, we're looking at a failed one-term presidency that the nation cannot afford.

Forget about electoral mandates or campaign promises. This president has a historic mandate. Just as Abraham Lincoln had to lead the nation from slavery and Franklin Roosevelt from the Depression, this president must lead the nation from the calamitous failures of three decades of conservative dominance. This requires beginning to reverse the perverse tax policies that have contributed to gilded-age inequality and starved the government of resources needed for vital investments. This demands correcting destabilizing global imbalances, laying a new foundation for reviving American manufacturing and shackling financial speculation. It means ensuring the United States leads rather than lags in the green industrial revolution. And it requires unwinding the self-destructive military adventures abroad. The president must strengthen America's basic social contract in a global economy, not weaken it.

This daunting project is not a matter of ambition or appetite - or even unconscious Kenyan socialism. It is the necessary function of a progressive president elected in the wake of calamitous conservative misrule. Every entrenched corporate and financial interest stands in the way; it is easier to take a less confrontational path. President Bill Clinton, for example, found it convenient to join in the conservative project of corporately defined trade, financial deregulation and social welfare constriction. From NAFTA to the repeal of welfare and the failure of labor law reform, to deregulating derivatives and repealing Glass-Steagall, he got his agenda wrong. He was seduced far more by Wall Street's Robert Rubin than by Monica Lewinsky.

Now Obama faces the same challenge. This isn't about conventional politics. This is simply about the fate and future of our country. This president has a clear and imperative historic mandate. If he shirks it, he risks more than failing to get reelected. He risks a failed presidency.

Katrina vanden Heuvel is editor and publisher of the Nation and writes a weekly online column for The Post.