Democrats broadened their control of Congress, though in the Senate they fell short of the 60 votes needed for a filibuster-proof majority that would have given them almost unbridled power over legislation.
Voters ousted Senate Republicans in North Carolina and New Hampshire and added three seats held by retiring GOP incumbents to the Democrats' fragile 51-49 majority.
Four other Senate races involving Republican incumbents remained too close to call Wednesday, including Georgia where a runoff election was scheduled and Minnesota where the margin was so close that state law forced a re-count. The GOP retained some leverage in spite of Democratic gains.
"The people have spoken. We hear the people and now it's time to come behind our president," Sen. Kay Bailey Hutchison, R-Texas, told "The Early Show" on CBS on Wednesday. "The Senate is going to have to work things out in a bipartisan way, and I think the test is going to be right there."
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In the Georgia Senate race between Republican incumbent Saxby Chambliss and Democratic challenger Jim Martin, each candidate won just shy of the 50 percent of the vote plus one required to win, so the state on Wednesday set a runoff election for Dec. 2.
In Minnesota, Republican Sen. Norm Coleman finished ahead of Democrat Al Franken in the final vote count, but Coleman's 571-vote margin falls within the state's mandatory recount law. That law requires a re-count any time the margin between the top two candidates is less than one-half of 1 percent.
Even as they celebrated Obama's election and their own victories, Democratic leaders pivoted to looming issues big and small, including whether to punish or tolerate a Senate ally who endorsed Republican John McCain. There were bigger questions down the road: how to resolve deep differences in their own ranks over promised reforms like universal health care and energy independence — and just how much the public would punish Democrats if they fail.
Too close to call
In Minnesota, Coleman and Franken were facing a lengthy wait for the results of a recount Wednesday after one of the state's tightest Senate elections ever.
With 100 percent of precincts reporting, Coleman led Franken by 570 votes out of nearly 2.9 million cast. Coleman had 1,210,940 votes to Franken's 1,210,370 votes.
Minnesota Secretary of State Mark Ritchie said the recount won't begin until mid-November at the earliest and will probably stretch into December. It will involve local election officials from around the state.
Franken, a former writer and performer on "Saturday Night Live", said his campaign was already looking into reports of irregularities in Minneapolis where some voters had trouble registering, though he wouldn't elaborate.
Franken said the margin was "four one-hundredths of one percent of the vote".
"There is reason to believe that the recount could change the vote tallies significantly," Franken added. "This has been a long campaign, but it is going to be a little longer before we have a winner."
Coleman's bid for a second term came against a strong Democratic headwind nationwide, led by Barack Obama's big presidential victory.
Overall, Democrats fattened their majority control of the Senate, ousting Republican Sens. Elizabeth Dole of North Carolina and John Sununu of New Hampshire and capturing seats held by retiring GOP senators in Virginia and New Mexico.
Piggybacking on the excitement level raised by presidential victor Barack Obama and his voter-registration and get-out-the-vote drives, Democrats increased their effective majority to at least 56 seats in the 100-member Senate.
"Obama ran a terrific campaign, he inspired millions of people," Senate Majority Leader Harry Reid of Nevada said in a telephone interview. "It's been a really good night."
All Democratic incumbents on the ballot prevailed.
Two other races with Republican incumbents remained to be resolved — in Alaska and Oregon.
But Republicans stopped a complete rout, holding the Kentucky seat of Senate Minority Leader Mitch McConnell and a Mississippi seat once held by Trent Lott — two top Democratic targets.
North Carolina state Sen. Kay Hagan, little known politically before her run, defeated Dole — a former Cabinet member in two Republican administrations and 2000 presidential hopeful. Dole had tried to tie Hagan, a former Presbyterian Sunday school teacher, to atheists in an ad that appeared to backfire.
Two Udalls win
In pair of western races, Reps. Tom and Mark Udall took over Senate seats held by retiring Republicans. Tom Udall, the son of former Interior Secretary Stewart Udall, defeated Republican Rep. Steve Pearce to succeed Pete Domenici in New Mexico. Tom's cousin Mark, the son of the late Rep. Morris Udall of Arizona, won the Colorado seat held by Republican Wayne Allard, who did not seek re-election.
Former Democratic Gov. Mark Warner breezed to victory in Virginia to take a Senate seat held for five terms by retiring GOP Sen. John Warner, beating another former governor, Republican Jim Gilmore. The two Warners are not related.
Democratic Sen. Mary Landrieu of Louisiana, the only serious GOP target, won her re-election over Republican state treasurer John Kennedy.
"Winston Churchill once said that the most exhilarating feeling in life is to be shot at — and missed," McConnell said late Tuesday. "After the last few months, I think what he really meant to say is that there's nothing more exhausting."
GOP wins in Mississippi
In a tight Mississippi contest, Republican Roger Wicker, squeaked past former Democratic Gov. Ronnie Musgrove to serve another four years of the term originally won in 2006 by Lott. Wicker was appointed to the post temporarily after Lott stepped down.
With Warner's victory in Virginia, Democrats now control both Senate seats and the governor's mansion. Virginia usually votes Republican in presidential elections, but Obama also won there Tuesday.
Democrats had counted on a slumping economy, an unpopular war and voter fatigue after eight years of President Bush to bolster a razor-thin 51-49 effective majority they've had the past two years after adding six seats in 2006.
They set a sky's-the-limit goal of controlling 60 Senate seats when the new Congress convenes in January — the magic number needed to prevent Republicans from blocking bills and judicial nominees. It was always a long shot.
But having a majority in the high 50s will enable Democrats to exercise far more control than they have now, since some Republicans probably would join them in efforts to break Senate logjams on many bills and judicial appointments.
But some observers believe hard-line Democrats hoping to bring a unified party to the new Senate may be disappointed.
Many of the new Democratic senators will more than likely bring some of their state's conservative values to the Senate and may vote against the party line on some social and economic issues. Also, the conservative Democrats already in the Senate sometimes vote with Republicans. That group includes Democrats from Nebraska, Montana, Louisiana, West Virginia and both Dakotas.
As the Cook Report's Jennifer Duffy explained it, "There are enough Democrats who abandon the party's position on any given issue to make 60 something of a false number."
Still, Democrats will wield more control in committees because committee membership is proportional to the size of the Senate majority. Currently, the Democrats' slim majority translates into a one-seat advantage on almost every committee. But the Democrats could pick up as many as two more seats per committee. The final numbers are negotiated with Senate Republican leaders.
Sen. Joe Lieberman of Connecticut, one of two independents who align with Democrats, is threatened with the loss of his chairmanship of the Homeland Security and Government Affairs Committee as payback for actively supporting the presidential bid of Republican Sen. John McCain. Reid, the majority leader, said he would meet with Lieberman later in the week to discuss the matter.
"Now that the election is over, it is time to put partisan considerations aside and come together as a nation to solve the difficult challenges we face and make our blessed land stronger and safer," Lieberman said in a written statement. He had harshly criticized Obama in a speech at the GOP nominating convention in September.
Democrats will also lose two incumbents: Obama and Biden. Democratic governors in Illinois and Delaware are sure to appoint Democrats to replace them.
Democrats had fewer seats to defend than Republicans. Of the 35 races on Tuesday's ballot, 23 were held by Republicans, 12 by Democrats.
Another possible pickup for Democrats: Sen. Ted Stevens, R-Alaska. Stevens, at 84, the longest serving Republican in Senate history, sought re-election despite calls from GOP leaders to resign after he was convicted last week of seven counts of lying on Senate financial disclosure forms.
He was locked in a tight contest with Democrat Mark Begich, the mayor of Anchorage.
With more than 40,000 absentee ballots to be counted within 10 days of the election, Stevens went home late Tuesday to get some sleep, his political future uncertain.
Republican Sen. Gordon Smith in Oregon was also on the list of Democratic targets.
Republicans held the Nebraska seat of retiring Sen. Chuck Hagel, with former Gov. Mike Johanns defeating Democrat Scott Kleeb, a college history instructor. Johanns resigned as Bush's agriculture secretary to make the race.
Republicans also held the Idaho seat of Sen. Larry Craig, who decided not to run for re-election after he was caught last year in a men's room sting. Idaho Lt. Gov. Jim Risch won the seat.
Republican incumbent senators who cruised to re-election included Lindsay Graham in South Carolina, Susan Collins of Maine, Jeff Sessions in Alabama, James Inhofe in Oklahoma, Lamar Alexander in Tennessee, Pat Roberts in Kansas, Thad Cochran of Mississippi, John Cornyn of Texas and Michael Enzi in Wyoming. Sen. John Barrasso, appointed after Wyoming Sen. Craig Thomas died, was elected to fill the remaining four years of Thomas' term.
Democratic senators easily winning re-election included Jay Rockefeller of West Virginia, Dick Durbin of Illinois, John Kerry of Massachusetts, Frank Lautenberg of New Jersey, Carl Levin of Michigan, Tim Johnson of South Dakota, Mark Pryor of Arkansas, Max Baucus of Montana, Tom Harkin of Iowa and Jack Reed of Rhode Island.
NBC News and The Associated Press contributed to this report.