On, CBS News estimates Democrats have picked up three of the six seats – Ohio, Pennsylvania and Rhode Island – they need to take control.
Key Senate races in Montana, Virginia, Tennessee and Missouri remained too close to call; Democrats need to win three of these races.
Sen. Rick Santorum of Pennsylvania, the No. 3 Republican in the Senate and one of its most conservative members, was a projected loser after two terms to Bob Casey Jr., the state treasurer. In Ohio, Sen. Mike Dewine lost to Democrat Sherrod Brown, a congressman strongly opposed to free-trade agreements, CBS News estimates.
In Rhode Island, Democrat Sheldon Whitehouse was the projected winner over Republican Sen. Lincoln Chafee.
Democrats were projected to hold two Senate seats they were in danger of losing, with Sen. Robert Menendez winning reelection in New Jersey and Rep. Ben Cardin winning a vacant Senate seat in Maryland.
In the comeback story of the night, Sen. Joe Lieberman of Connecticut, who ran as an independent after losing to businessman Ned Lamont in the Democratic primary, will defeat Lamont in the general election, CBS News estimates.
In a close contest in Arizona, CBS News estimates Republican Sen. Jon Kyl will hold his seat.
On the House side, Republican incumbents went down in nearly every region of the country. Three GOP congressmen were projected losers in Indiana, two in New Hampshire, one in North Carolina, and a Democrat won an open seat in Arizona.
Ethics woes were clearly taking their toll on the GOP.
Republicans surrendered the Ohio seat once held by Bob Ney, who resigned after pleading guilty in a lobbying scandal, and the Florida seat of Mark Foley, who stepped down after the disclosure that he sent sexually explicit messages to male congressional pages.
In Pennsylvania, Democrats defeated Curt Weldon in the fallout from a federal corruption investigation and Don Sherwood who admitted to a long-term affair with a much younger woman who says he choked her.
"We are on the brink of a great Democratic victory," said House Minority Leader Nancy Pelosi of California — in line to become the first woman speaker in history.
Despite the victory, Pelosi faces a tough job ahead.
"The margin of victory could be very small. We're not seeing the tsunami that was predicted," said CBS News political consultant Dotty Lynch. "A win is a win, and the party in power can pick the important chairman of committees. But a lot of the Democrats elected are conservative democrats so that complicates things. The job of the majority leader will be complicated."
Exit polls showed thewas shaping up as a nationalized election, with most voters saying national issues outweighed local ones.
Most said President Bush was a factor in their vote, and more are casting ballots to oppose him than to support him. Most voters said they were angry or dissatisfied with the administration.
As expected, voters who support the Iraq war are backing Republicans and those who disapprove of it are backing Democrats. Disapproval of Congress is high and that is helping Democrats overall.
"It is all about the president and the war in Iraq," said CBS News chief Washington correspondent Bob Schieffer.
Most voters said they had made up their minds about their votes last month or before.
"We're seeing a huge turn in independent voters to the Democrats," said CBS News political consultant Stu Rothenberg. "National exit polls show a significant advantage for Democratic candidates."
History worked against the GOP, too. Since World War II, the party in control of the White House has lost an average 31 House seats and six Senate seats in the second midterm election of a president's tenure in office.
Across the country, both parties hustled to get their supporters out in high-stakes contests across the country — Democrats appealing one more time for change and appearing confident the mood was on their side. But Republicans were conceding nothing as their vaunted get-out-the-vote machine swung into motion.
President Bush was at the White House, awaiting returns that would determine whether he would have to contend with divided government during his final two years in office.
Voting at sunrise, Mr. Bush switched from partisan campaigner to democracy's cheerleader as he implored Americans of all political leanings to cast ballots. (
"We live in a free society, and our government is only as good as the willingness of our people to participate," said Mr. Bush, his wife, Laura, at his side and an "I Voted" sticker on the lapel of his brown suede jacket. "Therefore, no matter what your party affiliation or if you don't have a party affiliation, do your duty, cast your ballot and let your voice be heard."
Several veteran senators coasted to new terms, including Republicans Orrin Hatch in Utah, Richard Lugar in Indiana, Trent Lott in Mississippi and Olympia Snowe in Maine; Kay Bailey Hutchison in Texas, Craig Thomas in Wyoming; and Democrats Robert C. Byrd in West Virginia; Edward M. Kennedy in Massachusetts; Tom Carper in Delaware; Debbie Stabenow in Michigan; Herb Kohl in Wisconsin; Jeff Bingaman in New Mexico, Ben Nelson in Nebraska and Kent Conrad in North Dakota and John Ensign in Nevada.
In Florida, Bill Nelson thumped former secretary of state Katherine Harris to win a second term.
Sen. Hillary Rodham Clinton coasted to a second Democratic term in New York, winning roughly 70 percent of the vote in a warm-up to a possible run for the White House in 2008.
Democrats also won a majority of, including Massachusetts, Deval Patrick becomes the state's first black chief executive.
Other estimated statehouse winners: Democrat Janet Napolitano in Arizona, Republican Rick Perry in Texas, Republican Dave Heineman in Nebraska, Democrat Bill Richardson in New Mexico, Democrat Eliot Spitzer in New York and Democrat Dave Freudenthal in Wyoming.
Voters also filled state legislative seats and decided hundreds of statewide ballot initiatives on issues ranging from proposed bans on gay marriage to increases in the minimum wage.
About a third of voters nationwide were using new equipment, andwere reported right out of the gate. The government deployed a record number of poll watchers to the many competitive races across the country.
Overall, the Justice Department said polling complaints were down slightly from 2004 by early afternoon.