Democrats took Senate seats away from Republicans in Ohio, Rhode Island and Pennsylvania on Tuesday but the GOP battled hard to retain its control of the chamber.
Seizing on voter discontent with President Bush and the war in Iraq, Democrats faced an uphill fight in trying to end Republican rule with a handful of races still undecided.
In Pennsylvania, Democrat Bob Casey, son of a popular former governor, soundly defeated incumbent Sen. Rick Santorum, a conservative and third-ranking member of the Senate GOP leadership. Democratic Rep. Sherrod Brown easily beat GOP incumbent Mike DeWine in Ohio, a state where Republican scandals were devastating for the party.
Former state Attorney General Sheldon Whitehouse defeated incumbent Sen. Lincoln Chafee in Rhode Island. Chafee is an openly anti-war Republican who consistently voted against President Bush on legislation.
Democrats needed to pick off at least three more Republicans among competitive races in Virginia, Tennessee, Missouri and Montana. Republicans, however, held leads in all but Montana.
"I think we will hold control of the Senate," Republican National Chairman Ken Mehlman said on CNN.
Democrats were far from throwing in the towel. "We're not breaking out the champagne bottles yet. It's going to be a long night, but so far, so good," New York Sen. Chuck Schumer, chairman of the Senate Democrats' campaign operation, told supporters.
Even if they don't get a majority, Democrats will make it harder for Bush to enact his agenda his final two years in office by holding more seats in the Senate.
Sen. Joseph Lieberman, the Democrats' vice presidential candidate in 2000 but running as an independent after losing the Democratic primary, kept his seat from Connecticut.
In New Jersey, Sen. Bob Menendez held off a strong challenge from Republican Tom Kean Jr., son of a former governor, to keep the seat in Democratic hands. Menendez had been viewed as the most vulnerable of 17 Senate Democrats seeking re-election.
Democrats also kept their seat in another important race in Maryland, where Rep. Ben Cardin held off a late surge by Republican Lt. Gov. Michael Steele to succeed retiring Sen. Paul Sarbanes.
Former First Lady Hillary Rodham Clinton, considering a Democratic bid for the White House in 2008, easily won re-election to a second term from New York.
Lieberman will be one of two independents in the new Senate. Rep. Bernie Sanders, an eight-terms congressman who calls himself a socialist, won the seat of retiring Sen. Jim Jeffords, also an independent. Both Lieberman and Sanders have said they will align themselves with Democrats.
Democratic Sens. Dianne Feinstein of California, Maria Cantwell of Washington and Debbie Stabenow of Michigan were re-elected. Democrats also kept seats in Wisconsin, North Dakota, New Mexico, Michigan, Nebraska, West Virginia, Massachusetts, Florida, Delaware, Wisconsin and Hawaii.
Republican Sen. John Kyl won re-election in Arizona despite Democratic hopes for an upset by wealthy businessman Jim Pederson.
Republicans also won re-election in Indiana, Maine, Mississippi, Wyoming, Texas, Utah and Nevada.
In Florida, Democratic Sen. Bill Nelson handily rebuffed a challenge from Republican Rep. Katherine Harris, a two-term House member.
Harris came to national attention in 2000 when, as Florida secretary of state, she certified Bush as the Florida winner in his nearly deadlocked presidential race with Democrat Al Gore. However, she fell out of favor with Florida Republicans, and was even urged by Florida Gov. Jeb Bush, the president's brother, not to run.
Democrats needed a net gain of six seats to take control of the Senate, which, except for a 19-month period in 2001 and 2002, has been run by Republicans since 1995.
Exit polls showed that almost six in ten voters disapproved of the war in Iraq, and an equal percentage said they disapproved of how President Bush was handling his job.
In Pennsylvania, about half of those who said in exit polls that they voted for Casey characterized their votes being primarily against Santorum rather than a vote for Casey. Casey also got a boost from one-third of voters who said they were angry with Bush. One-fourth of them said they were mad at GOP leaders in Congress.
Ohio voters expressed similar views. About six in 10 Brown voters said their vote was intended to register opposition to Bush. Two-thirds of Brown voters said they disapproved of the way Congress was handling its job.
Sen. Elizabeth Dole of North Carolina, who leads the Senate Republican campaign effort, said that voter turnout was heavy across the country. She said it was particularly big in Montana and Missouri.
"I think this is great for us," she told reporters.
Amy Klobuchar, a prosecutor, kept the seat of retiring Sen. Mark Dayton in Minnesota in Democratic hands, defeating Republican Rep. Mark Kennedy.
In Virginia, Republican incumbent George Allen held a small but significant lead over Democrat Jim Webb, a former Navy secretary under President Reagan, with four-fifths of the state's precincts reporting.
In Tennessee, Republican Bob Corker, a former mayor of Chattanooga, took an early lead over Democratic Rep. Harold Ford, who sought to become the first black Southerner elected to the Senate in more than a century. The two were vying for the Republican seat now held by retiring Senate Majority Leader Bill Frist.
Republican Sen. Jim Talent also took an early lead in Missouri over Democrat Claire McCaskill, the state auditor.
Among incumbents who coasted to re-election were liberal Democratic lion Edward M. Kennedy of Massachusetts West Virginia Sen. Robert C. Byrd, who has spent more than half of his 88 years in the Senate.
Veteran Republican senators coasted to re-election in five states: Richard Lugar in Indiana, Olympia Snowe in Maine, Trent Lott in Mississippi, Kay Bailey Hutchison in Texas and Orrin Hatch in Utah.
In Wyoming, Republican Craig Thomas, though hospitalized with pneumonia, won re-election to a third term. And Republican Sen. John Ensign in Nevada turned back a challenge from Democrat Jack Carter, son of former President Jimmy Carter.
Other Democrats winning re-election included Tom Carper in Delaware, Jeff Bingaman in New Mexico, Ben Nelson in Nebraska, Herb Kohl in Wisconsin, Kent Conrad in North Dakota and Daniel Akaka in Hawaii.