For up-to-the-minute results in all of today's races, check out ABC News' ELECTION SCORECARD
OHIO: Democrat Sherrod Brown unseated incumbent Republican Sen. Mike DeWine. As in many other states, exit polls show this race was largely a referendum on Bush: Six in 10 voters there disapproved of the president's performance, and of those, more than 85 percent voted Democratic in the Senate race.
In Ohio's gubernatorial race, Democrat Ted Strickland appears to have beaten Republican Kenneth Blackwell in an open contest. This was a governorship that had been in Republican hands.
CONNECTICUT: Sen. Joe Lieberman, running as an independent, defeated Democratic challenger Ned Lamont -- even though Lamont had beaten him in the Democratic primary. Lieberman has vowed to vote with the Democrats in the Senate.
NEW JERSEY: Democratic Sen. Robert Menendez defeated Republican challenger Thomas Kean Jr. This was a campaign that Democratic managers said they had to hold if they had hopes of winning a majority in the Senate.
Elsewhere, veteran Senate Democrats coasted to re-election -- Hillary Rodham Clinton in New York, Ted Kennedy in Massachusetts, and Robert Byrd in West Virginia. Debbie Stabenow, the Democratic incumbent in Michigan, held on despite the state's economic woes.
Many Republican incumbents were easily returned to office: Sens. Kay Bailey Hutchinson in Texas, Trent Lott in Mississippi, and Olympia Snowe in Maine, among others. Richard Lugar easily kept his seat in Indiana; Democrats did not challenge him.
In a close race, Republican Jon Kyl held onto his Senate seat in Arizona, beating out Democratic challenger Jim Pederson.
Republican governors Arnold Schwarzenegger of California, Rick Perry of Texas, Sonny Perdue of Georgia, Bob Riley of Alabama and Mark Sanford of South Carolina have all been re-elected.
In Florida, Republican Charles Crist won the seat being vacated by Jeb Bush, the president's brother.
While Democrats made gains, that did not necessarily mean that liberalism did. Several states -- including Colorado, Idaho, Wisconsin, Virginia, South Carolina and Tennessee -- passed referenda defining marriage as the union between a man and a woman, rejecting calls to legalize gay marriage.
In Michigan, voters passed a proposition banning public institutions from considering race or sex in hiring or college admissions -- a defeat for advocates of affirmative action programs.
On the other hand, a measure to ban abortion in South Dakota was defeated.
Parties that hold the White House tend to lose congressional seats at midterm -- but George W. Bush has the lowest approval rating of any president at this point since Harry Truman in 1950. Six out of 10 people told exit polls they disapprove of Bush's performance in office and 61 percent of them said they were unhappy with the job that Congress was doing.
Take, for instance, New Jersey -- a state where both major candidates hurled attack ads at each other. Both messages stuck -- and the Democrat won, anyhow.
Republican Thomas Kean Jr., son of a popular former governor, said Democrat Bob Menendez was corrupt and people could expect "more federal investigations" if Menendez won.
Menendez, for his part, painted Kean as a rubber-stamp vote for the Bush administration -- never mind that Kean supported federal funding for stem-cell research, and called for the resignation of Defense Secretary Donald Rumsfeld.