Voters dealt a devastating blow to Senate Democrats in Tuesday’s elections while greatly enhancing Republican power in Congress and the ability of social conservatives and business to advance their agendas.

In a single stroke, Senate Democratic Leader Tom Daschle was defeated in South Dakota and Republicans gained four Senate seats, putting them within striking distance of the 60-vote supermajority needed to limit debate and expedite action on contentious legislation.

With a few races still in dispute in the House, Republicans hope to gain three to four seats on top of their current 12-vote advantage in that chamber. But it is the new 55-vote Senate Republican majority that will have the most immediate effect on everything from the future makeup of the Supreme Court to business-backed bills to restrict lawsuits.

Fiscal conservatives already feel emboldened to demand more dramatic changes in federal-benefit programs in the face of record deficits and the mounting costs of the Iraq war. At the same time, Democratic moderates might lose some of their nerve to stand in the way.

"Fifty-five votes. It’s a big change and means we can go to the floor with the confidence of winning," said Sen. Judd Gregg, a New Hampshire Republican, who appears eager to take on the challenge of leading the Senate Budget Committee.

By chance, the elections coincide with turnover among Senate committees under relatively new rules that set six-year term limits for most chairmanships. Sen. Thad Cochran of Mississippi, for example, already is slated to take over the Senate Appropriations Committee, and if Gregg were to take the Budget Committee chairmanship as now expected, Sen. Michael Enzi, a Wyoming accountant with an interest in pension legislation, would likely succeed him as chairman of the Senate Health, Education, Labor and Pensions Committee.

Rather than wait until the new Congress is seated next year, business interests are looking at the option of striking quickly to pass a long-sought class-action bill in the lame-duck session later this month.

"It’s clear the results of the election show that the American people care about this issue of legal reform and frivolous lawsuits," said Stan Anderson, the U.S. Chamber of Commerce’s executive vice president. "We’re going to be even more aggressive than we’ve been in pushing our agenda."

Tuesday’s results fulfill a historic transformation of the South, from an old Democratic power base in Congress to one belonging more and more to Republicans. Among Senate newcomers is David Vitter, who will be the first Republican senator to represent Louisiana since Reconstruction.

With the exception of Daschle’s defeat, almost all the Republican gains in the Senate can be explained by races in which Republicans picked up seats being vacated by Southern Democrats, some of whom, like Sen. Ernest Hollings of South Carolina, first came into office as long ago as 1966. Republicans repeated the pattern in North Carolina, Florida and Georgia, leaving Sen. Blanche Lincoln, who won a second term in Arkansas, as the only Democrat to win in a Southern Senate race on Tuesday.

The South’s influence extends to the House, where Majority Leader Tom DeLay helped engineer a redistricting plan in his home state of Texas that proved disastrous for even senior Democrats like Reps. Charles Stenholm and Martin Frost, who have a combined record of 52 years in the House.

Reps. Nick Lampson and Max Sandlin also were unseated in Texas, and the state’s 32-member House delegation-now evenly split between the two parties-will be 21-11 in favor of Republicans.

The Southern influence brings a greater social conservatism and evangelical Christian influence that are certain to affect deliberations on federal judges and nominees for the Supreme Court.

Senate Majority Leader Bill Frist of Tennessee, who has presidential ambitions for 2008, already is courting his party’s socially conservative wing. So is Pennsylvania Sen. Rick Santorum, a second member of the leadership with an eye on the White House.

If his fellow Pennsylvanian, Sen. Arlen Specter, gets the Judiciary Committee chairmanship, he will have some moderating influence. But with 55 votes now, Senate Republicans are in a position to expand their one-vote margins on most Senate committees like Judiciary, and the chairman alone won’t be able to halt action on a nominee.

After losing Daschle, Democrats face a period of soul-searching over what direction to take and whom to choose as party leader.

Sen. Harry Reid, the Democratic whip who was re-elected in Nevada Tuesday, already has served notice that he hopes to succeed Daschle as minority leader. A soft-spoken consummate insider, Reid has done enough favors for his colleagues to be the front-runner, but a fight could break out over his No.2 spot that will give some insight into what tack Democrats will take next.

There could be a leftward tilt since many of the Southern Democrats leaving the Senate, like Louisiana Sen. John Breaux or Hollings of South Carolina, had been to the right of many in the party caucus. But the diverse group of Democratic newcomers elected Tuesday don’t share any particular ideology.

Illinois is sending Democrat Barack Obama, who will be the only black senator in the new Congress; he won a national following after his keynote speech at the Democratic convention in Boston. And Colorado made history by electing Ken Salazar, the Democratic state attorney general and a Mexican-American, to the Senate on the same night his brother John, a farmer and one-term state legislator, won a seat in the House.

By chance, the elections coincide with turnover among Senate committees under relatively new rules that set six-year term limits for most chairmanships. Sen. Thad Cochran of Mississippi, for example, already is slated to take over the Senate Appropriations Committee, and if Gregg were to take the Budget Committee chairmanship as now expected, Sen. Michael Enzi, a Wyoming accountant with an interest in pension legislation, would likely succeed him as chairman of the Senate Health, Education, Labor and Pensions Committee.

Taking his cue from President George W. Bush, Republican Leader Frist sought to play down the partisanship of the campaign and focus more on coming together.

"The election is over. Our nation is at war," he said in a statement late yesterday. "It’s time to overcome our differences, lay aside the rancor and get to work."

Voters only have to wait until the lame-duck session in two weeks to see if that is the case.