A day after winning a rare White House victory with Congressional coattails, exuberant Republicans on Capitol Hill laid claim to a new mandate for legislative action even as they tried mightily not to succumb to triumphalism.

But they also issued a warning to the vanquished Democrats, pointing to the fate of Senate Minority Leader Tom Daschle (D-S.D.), who became the first Senate leader in five decades to lose his seat — in large part, the Republicans argue, because of his efforts to stall portions of President Bush’s agenda.

In the words of Sen. George Allen (Va.), the National Republican Senatorial Committee chairman, “Obstructionism and petty partisanship [are] not acceptable to a majority of Americans.”

Senate Majority Leader Bill Frist (R-Tenn.) struck a similar theme in a statement released by his office. “In the Senate, where Republicans have gained four seats, I hope our expanded Republican majority will allow us to build working coalitions and put an end to the partisan roadblocks that have marred the past two years,” Frist said.

A senior Senate GOP aide said there is no doubt that voters empowered Congressional Republicans Tuesday night to try to seek approval on myriad issues ranging from Bush’s judicial nominees and a national energy policy to class action legislation that they charge Democrats blocked for partisan purposes.

“Clearly in the areas where Democrats obstructed, we have the opportunity to move forward and advance the issues for the good of America,” said the aide, who asked not to be named. The GOP aide suggested Democrats would need to review their strategy on policy matters in the wake of the devastating losses Tuesday night.

“Is our tack to continue to obstruct or do we need to be more accommodating?” the aide said Democrats must ask themselves. “Did our obstruction define us and force us to lose?”

While the election results moved Bush’s top two domestic priorities — reform of the tax system and Social Security — to the top of the agenda for the 109th Congress, there was a sense that even the Republicans’ newly enhanced majorities would lack the time, political capital and unity to complete both massive initiatives within one two-year cycle.

Republicans also seemed unsure of how the election’s outcome would affect the bitter fight on Capitol Hill over judgeships. While the GOP leadership’s argument is that the electorate repudiated the Democrats this week for blocking the president’s nominees, some conservatives wondered whether it would be pushing their luck to have previously sidelined nominees, such as Miguel Estrada and Priscilla Owen, renominated by the president.

Similarly, there is a question of whether the Republicans should move to permit some drilling for oil in the Arctic National Wildlife Refuge, one of the many controversial GOP priorities held over from the current Congress, as part of a larger energy bill.

Congressional Democrats, meanwhile, acknowledged that the party’s clear election losses had placed them firmly on the defensive for the time being.

“They are going to do what they are going to do,” said one senior Democratic aide who requested anonymity. “It is a pretty substantial victory. They are not going to come cowering into the next Congress.”

A Democratic insider predicted that Senate Republicans would seize on the election results to try to muscle through controversial bills, such as a constitutional ban on same-sex marriage, in the 109th Congress.

Congressional Republicans expect a chastened minority to put up fewer roadblocks, but they appeared to still be calibrating the extent of their mandate on Wednesday.

The four-seat pickup still left the GOP five seats short of the 60 votes needed to end a filibuster, and the narrowness of the presidential contest’s outcome made it difficult to know how aggressively the Republicans were willing to push agenda items that are controversial with Democrats and moderate Republicans.

Senate Majority Whip Mitch McConnell (R-Ky.) noted that despite its gains, the GOP still needs the support of Democrats to pass “major legislative” items.

“The math in the Senate does not change,” McConnell said in an interview. Setting a tone of magnanimity that was to be repeated throughout the day, he added, “The reality remains the same. To advance our agenda we need some help from the other” side.

While the results were certainly heartening to House Republicans, aides cautioned that the new partisan breakdowns don’t necessarily alter the legislative equation in the 109th Congress in a fundamental way.

“I don’t think [the agenda] would be any more aggressive than it otherwise would have been,” a senior House GOP leadership aide said. “You sort of get a little bounce in your step [from the results], but at the end of the day there still aren’t 60 votes in the Senate.”

Tax reform has gained momentum within the House GOP Conference in recent years, with dozens of lawmakers attaching themselves to various proposals. Yet Republican aides said that while sentiment in the House leans toward tackling the tax issue first, the White House will likely put Social Security reform first in line.

One challenge facing the tax-reform fight is that large sectors of the business community — retailers, in particular — are expected to fight any proposal to reform the tax system that puts businesses in the role of “tax collector.” That would make it difficult for Congress to even contemplate the much-discussed national sales tax. The Bush administration has indicated, in any case, that it will appoint a special commission to look at tax reform and come up with recommendations, a process that is expected to take as long as a year.

Beyond those major initiatives and the expected permanent extension of previously passed tax cuts, the future agenda is less clear.

While Bush won a clear majority of the vote Tuesday and does not have to worry about running again, House Republicans are already thinking about the next Election Day. With historical trends pointing toward a tough battle for the GOP to maintain its position in 2006, House Republicans are wary of adding more potentially controversial items to the docket.

“That creates the most angst in the House — the administration pushing something we don’t want them to push,” said a leadership aide, citing immigration reform as an example of an issue the White House may emphasize but which many Congressional Republicans would prefer not to tackle.

GOP strategists expect there to be numerous opportunities for variables, such as Supreme Court vacancies or sudden exigencies in the war on terror, to divert the process.

“It would be un-frickin’-believable if Congress could pass half those [GOP priorities] and have the president sign them into law,” said Bruce Josten of the U.S. Chamber of Commerce, citing a “crowding-out effect.”

Among other things, the president is expected to ask Congress soon for an additional $50 billion to $70 billion in emergency spending for post-war rebuilding in Iraq. Josten noted that Congress will need to reauthorize trade promotion authority by June — always a fitful task — and pointed out that next year offers a quintennial opportunity for Congress to demand that the United States withdraw from the World Trade Organization.

Any single Member can demand a resolution calling for the withdrawal. “And you know damn well that someone’s going to do that,” Josten said.

The retirement prospects of Supreme Court justices are perhaps the most tantalizing of the unknown variables. Court-watchers expect ailing Chief Justice William Rehnquist to leave the bench soon, and he could be followed by Justices Sandra Day O’Connor and John Paul Stevens.

Nicole Duran and Mark Preston contributed to this report.