By Thomas B. Edsall

Something odd happened on Capitol Hill this week. Something that seemed to start out as a publicity stunt — the House Democratic leadership’s 100-hour agenda — actually turned into a ...qualified success.

The passage of the Democrats’ eight-part legislative package — to be completed today — sets the stage for striking possibilities, some advantageous to the party, others threatening. In the short term, the leadership has achieved two goals:

First, Democrats have shown basic competence and authority after four decades of defeat and division, whether in the majority or minority.

Second, the House has now approved legislation directly addressing public concerns: raising the minimum wage, ethics reform, interest rate reductions on subsidized college loans and expanded federal support for stem cell research. It has put in place rule changes to promote fiscal responsibility and adopted recommendations from the 9/11 commission. Today, the House is expected to repeal tax breaks for oil companies. Poll-tested and guaranteed to be political winners, these achievements constitute a modest start toward a saleable centrist agenda for a party too often in the past labeled as extreme. More important in terms of substantive future legislation, the ability of the Democrats to win over significant numbers of Republicans on most votes signals the slim but enticing possibility of Democratic mastery over a demoralized Republican Party — one that has thrived on polarized partisan warfare in recent years.

If the new bipartisanship takes root, the prospects for health care legislation and immigration reform sharply improve. These proposals cannot survive without backing from both Democrats and Republicans. When it comes to health care, a key corporate lobby, the Business Roundtable, has already formed a tentative alliance with organized labor, thereby giving cover to wavering members of Congress from both ends of the political spectrum. A parallel alliance among business, Roman Catholic Church leaders and progressive organizations like the National Council of La Raza has already formed in support of immigration legislation.

Similarly, Republican willingness to cross the aisle strengthens the hand of those who want to build Congressional opposition to the Iraq war. Every Republican who joins the opposition makes it easier for Democrats in red states and districts to become public critics of the war, and for more Republicans to join with them. (Witness the suddenly outspoken Senator Gordon Smith of Oregon.) Without some measure of Republican support, Democrats who challenge the war — particularly those who vote to deny appropriations — run the risk of being portrayed as unpatriotic and unwilling to support American troops in the midst of battle.

The potential for Republican defection is a new thing. Conservatives have long recognized — and worked hard to prevent — the danger of a breakdown in party discipline. In 1993, William Kristol, then chairman of the Project for the Republican Future, orchestrated the defeat of the Clintons’ health care plan. In an influential memo, Mr. Kristol wrote: "Any Republican urge to negotiate a ‘least bad’ compromise with the Democrats, and thereby gain momentary public credit for helping the president ‘do something’ about health care, should also be resisted. ...The plan should not be amended; it should be erased." Judging from the early days of this Congress, however, Republican solidarity has begun to erode.

On another front, the restoration of Congressional bipartisanship may well have unintended consequences. Senator Barack Obama of Illinois has based his presidential campaign on a dysfunctional political system: "Politics has become so bitter and partisan, so gummed up by money and influence, that we can’t tackle the big problems that demand solutions," he told supporters this week.

Insofar as Congress regains efficacy, a compelling rationale of the Obama campaign is undermined. Senator Hillary Rodham Clinton, who has cast herself as working effectively within the system, can only benefit when the system appears to be functional. A functional Congress also potentially diminishes the taint of Washington tenure for candidates like Senator Joseph R. Biden Jr. of Delaware and former Senator John Edwards of North Carolina.

While there are upsides to the early success of House Democrats, they are by no means home free. Many Republicans see Democrats undermining themselves with the adoption of pay-as-you-go budget rules, which require new expenditures to be accompanied by equivalent spending reductions or tax hikes. At some point, Republicans argue, Democrats will be forced to make unwelcome cuts, raise taxes, or go back on their word. With these rules, argues Grover Norquist, president of Americans for Tax Reform, Democrats have set the stage to once again become the "tax and spend" party.

Mr. Norquist may have a point. A yet-to-be-released post-election poll of 36,000 respondents by the Cooperative Congressional Election Survey showed virtually no public support for a tax increase. Asked to pick alternative ways to reduce the deficit, 49 percent said they would cut domestic spending, 32 percent said they would cut defense spending and only 15 percent said they would raise taxes. For freshman Democrats who won seats in centrist states like Indiana and Kansas, support for a tax increase would probably be political suicide.

Many Democrats acknowledge that the pressure to raise taxes will intensify, especially if expensive health care programs make it onto the agenda. Nancy Pelosi, the House speaker, asked about taxes on "Face the Nation," said that any tax increase would be limited to the wealthy. Taking back "tax cuts for those making over a certain amount of money — $500,000 a year — might be more important to the American people than ignoring the educational and health needs of America’s children," she said. "We’re not going to start with repealing tax cuts, but they certainly are not off the table for people making over half a million dollars a year ... It’s an option, it’s not a first resort."

The Democratic Party is walking a tightrope. Arguably, the party had the last election handed to it on a plate — war, corruption, pederasty — what more could one ask for? In addition, voter repudiation of the president’s strategy in the Middle East does not mean Americans trust Democrats on national security.

There are plenty of other reasons to be skeptical of continued Democratic success. Middle-class anxiety about jobs, retirement and health care are in fact scarcely touched by the 100 hours. Race and ethnic prejudice have not evaporated. And George Bush won’t be here to kick around forever. Still, the first days of this new Democratic-led Congress turned out better than anyone might have expected. Given the party’s recent Congressional history, any success is notable — even if it’s only 100 hours long.