WASHINGTON — On the day before Christmas, President Obama found two presents under his tree. One was the health care reform bill passed that morning by the Senate, a historic measure so freighted with promise and problems that it could blow up.

The other was an op-ed article in the Washington Post by William Daley, his fellow Chicagoan and one of the canniest Democrats I know, warning Obama that he is on the verge of losing his grip on the vital center of politics.

Former Commerce Secretary Daley, who shares with his brother, Mayor Richard M. Daley, and their late father an iron grip on reality, cited all the signs of defection among swing voters whose support in 2006 and 2008 swelled Democratic ranks in Congress and elected Obama. He ticked off the losses Democrats suffered in the only two gubernatorial elections of 2009, in New Jersey and Virginia; the polls showing independents rejecting Democrats (and such handiwork as the health care bill); a wave of early retirements by marginal House members; and, last week, the party switch by Alabama Rep. Parker Griffith from Democrat to Republican.

To be sure, there are counter-indicators not mentioned by Daley, including a string of special election congressional victories for the Democrats, culminating in New York's 23rd District. The Republican civil war that enabled this upset is symptomatic of a growing GOP liability that could cripple the party's comeback hopes.

But this does not weaken the thrust of Daley's main argument. His target is the left of his party — the grass-roots liberal activists who condemn the centrist Democrats sitting in marginal seats for blocking some provisions of health care reform, for example, and the leaders of organized labor who threaten to retaliate by withholding their support from the moderates.

These same groups put heavy pressure on Obama to move his agenda to the left — even when a Congress with swollen Democratic majorities is balking at the measures Obama already has endorsed.

The president is surrounded by people who share Daley's grip on reality, none more important or better placed than Rahm Emanuel, the chief of staff and another fellow Chicagoan. But the picture is not so clear on the other end of Pennsylvania Avenue.

Speaker Nancy Pelosi's inner circle is made up of long-standing veterans of gerrymandered House districts, virtually immune from Election Day challenge, just as she is. The wants and needs of "the Democratic base" count heavily for them, and Daley's warnings may be resented or ignored.

Senate Majority Leader Harry Reid's home-state party in Nevada is as closely tied to the unions as Michigan used to be in the days of Walter Reuther, and Reid views the world from that perspective.

As a loyal Democrat, Daley insisted in the closing paragraphs of his op-ed that his party is not doomed to ruin. It still can avoid anything more than a minimal setback in 2010, he said, if it will simply "acknowledge that the agenda of the party's most liberal supporters has not won the support of a majority of Americans — and, based on that recognition . . . steer a more moderate course on the key issues of the day, from health care to the economy to the environment to Afghanistan."

I am not so certain. It will be up to Obama to steer the Democrats in that direction. No one on Capitol Hill is likely to lead such a change. The first test will come with the revisions of health care in the House-Senate conference, whether the White House insists on strengthening the cost-saving measures in the bills.

The larger tests will lie in Obama's 2010 State of the Union and budget messages — whether he fulfills his promise to start addressing the runaway budget deficits left in the wake of the recession. A presidential endorsement of the much-discussed commission empowered to slow the hemorrhage of red ink would signal to voters that Daley's message has been heard.

David Broder is a Washington Post columnist.