Sen. Harry Reid (D-Nev.) gained an expanded Senate majority Tuesday night, and the country may have given Democrats a mandate for their agenda, but it remains unclear how the strengthened Majority Leader will turn this momentum into legislative gold in the next few months.

Reid also has a tough decision on whether to take actions that could reduce the five seats that he has already gained by one. Reid is expected to meet with Sen. Joe Lieberman (ID-Conn.) in Washington, D.C., today, presumably to talk about whether Lieberman should remain chairman of the Homeland Security and Governmental Affairs Committee after he aggressively criticized President-elect Obama and endorsed GOP nominee Sen. John McCain (Ariz.).

With or without Lieberman, Reid will have a majority of at least 55 and possibly more if any of three Senate races that are close but undecided turn in Democrats’ favor. At press time, Sen. Saxby Chambliss (R-Ga.) appeared to be headed into a Dec. 2 runoff, giving the Democrats a chance for another potential pickup.

Even with that decisive majority, Reid appeared to be laying the groundwork to govern from the middle. Reid said repeatedly Tuesday night that the election did not provide a mandate for Democrats, but for bipartisanship. His first test will come Nov. 17 during the lame-duck session, when Democrats in both chambers attempt to move a massive appropriations bill designed to stimulate the economy, but it’s already looking like a heavy lift.

Senate Minority Leader Mitch McConnell’s (R-Ky.) re-election Tuesday makes it likely that the makeup of the Senate leadership in both parties will stay the same — raising the question of whether two years of legislative gridlock can be overcome when the parties doing the negotiating haven’t changed.

Democrats warned that though they hope Republicans will see the election as cause to re-evaluate their objections to another stimulus package, among other things, it appears the GOP is retrenching by calling for a return to the party’s fiscally conservative roots.

“We’re still waiting for a clear signal from the Senate Republicans … and the White House about whether they’re willing to sit down and negotiate,” Reid spokesman Jim Manley said. “If not, the American people will once again lose under the Republicans’ failed economic policies.”

Other Senate Democrats, however, said Reid has an opportunity in the lame duck to leverage his gains into passage of a stimulus package, despite the fact that his new Members will not be seated until January. One senior Senate Democratic aide suggested that Republicans may make the calculation, with or without Reid’s prodding, that passing a stimulus this year would save them from passing an even larger spending package next year when the economy could be in worse shape.

Even in the unlikely case that Senate Republicans go along with a stimulus bill during the lame duck, Reid still has to deal with a stubborn Republican White House that has been reluctant to sign onto any new economic stimulus package.

“I certainly hope that the president will be on board with us,” Sen. Bob Menendez (D-N.J.) said of President Bush. “He can’t be completely tone deaf to where the American people are in this election on the economy.”

Sen. Debbie Stabenow (D-Mich.) agreed and indicated that Senate Democrats were prepared to scale down their proposal to get at least some of what they want. “We don’t expect to get everything we think is important for a stimulus,” she said.

But she warned that Bush might push for enactment of a controversial trade pact with Colombia.

“The question is what’s the price for that” White House cooperation, Stabenow said. “Is that a price we really want to pay?”

After the new Members are seated in the 111th Congress, Senate Democrats say they feel certain that they will get more cooperation from Republicans to move legislation, given they will only need to pick off five or fewer Republicans — rather than the nine that eluded them for the past few years — to break a filibuster.

“I feel confident we’re going to be able to move things,” Reid said in an interview Tuesday night.

Stabenow said the first bills to be taken up next year would likely include passage of a children’s health insurance bill that Bush vetoed, more spending for infrastructure and a measure focused on expanding “green jobs” and alternative energy production. Menendez said Democrats would move quickly to pass a budget resolution that would lay the groundwork for economic policy and spending options.

Though Reid and McConnell get along personally, they clashed repeatedly over procedural matters, particularly over the rights of Republicans to offer amendments — a situation that led the Senate GOP to block to a record number of bills from coming to the Senate floor in the 110th Congress.

Reid said it would be “foolish” for Senate Republicans to continue their attempts to block legislation in the chamber.

He noted that moderate Maine Republican Sens. Susan Collins, who won re- election Tuesday night, and Olympia Snowe could be decisive votes for Democrats.

“They’re not going to be able to filibuster now,” Reid said. “We have a few Senators from Maine, and we’re going to have [Arizona Sen.] John McCain, who’s never been a filibusterer.”

Stabenow added that if Sens. Gordon Smith (R-Ore.) and Norm Coleman (R-Minn.) return to the Senate, they too will be swing votes who Democrats could potentially draw on. (By late Wednesday, Smith and Coleman were still locked in races that were too close to call.)

“A lot of people in both parties have been frustrated by the obstruction,” Stabenow said. “For the last two years, a majority of Republicans went along with their leadership on that. … The question is whether [centrists] will choose to put their fortunes with colleagues who are continuing to obstruct.”

Reid said he believes the newly elected Senators will feel, as he does, that the country voted Tuesday night for moderate — not liberal — policies, despite Democrats’ gains.

“I think the country has moved to the center,” Reid said. “I think people want us to get things done.”

Despite the call for bipartisanship, Reid is under increased pressure from his rank and file to punish Lieberman’s disloyalty to the party. Though most Democratic sources say Lieberman will likely not be kicked out of the Senate Democratic Conference, the act of taking away his chairmanship could cause him to switch parties — a scenario that he has not completely ruled out.

Lieberman told a conservative radio commentator on Election Day that he feared the idea that Senate Democrats would reach a filibuster-proof majority by winning 60 seats. He warned that without at least 41 Republicans to stop “the passions of the moment,” the country’s well-being could suffer under Democratic rule.