Republicans gained a symbolic victory in Illinois, nabbing the Senate seat formerly occupied by President Obama, and won in a number of key states as more Democratic incumbents fell prey to voter discontent Tuesday.
GOP candidate Mark Kirk will beat Democratic state treasurer Alexi Giannoulias, according to ABC News projections, in a race that was considered a dead-heat until the very end. Independents have generally voted for the Democratic Senate candidate in previous elections except in 1998. But this year, they went for Kirk by a large margin, 58-29 percent.
President Obama enjoys a 55 percent favorable rating among these voters, one of his best in any state, but 16 percent of those who voted for Obama in 2008 crossed over to Kirk this year.
In Pennsylvania, another Democratic stronghold, Republican candidate Pat Toomey was projected to defeat Democrat Joe Sestak, who beat longtime Sen. Arlen Specter in a bitter battle earlier this year. The poor economy and government dissatisfaction played to Toomey's favor.
Russ Feingold, D-Wis., was projected to become the second Democratic senator to be defeated, after Sen. Blanche Lincoln of Arkansas, who became a casualty earlier Tuesday evening, according to ABC News projections.
There was one bright spot for Democrats on the West Coast, where Sen. Barbara Boxer, another Democrat who ran a tight race against ex-Hewlett Packard chief executive Carly Fiorina, is projected to retain her seat. Senate Majority Leader Harry Reid is also projected to continue in his position despite a bitter battle that nearly put the longtime senator out of office.
Republicans are so far projected to take six seats from the Democrats. In addition to Arkansas, the GOP appears to have scored a key victory in another Democratic stronghold, North Dakota, where Gov. John Hoeven will become the first GOP senator from the state in 24 years. The Republican will replace retiring Sen. Byron Dorgan, a moderate Democrat who has occupied that seat for 18 years.
Across the country: Republicans have so far gained Senate seats in Illinois, Pennsylvania, North Dakota, Arkansas, Indiana and Wisconsin. They've held on to Senate seats in South Dakota, Kansas, Oklahoma, Iowa, Missouri, Louisiana, Ohio, Kentucky, Alabama, Georgia, Florida, South Carolina, North Carolina, New Hampshire, Arizona, Utah and Idaho.
The Tea Party has scored major victories in an election dominated by U.S. economic woes. Republican Marco Rubio will win the Florida Senate race by a wide margin and GOP candidate Rand Paul will win the Kentucky Senate race, according to ABC News exit-poll results.
In Indiana, according to ABC News projections, Tea Party favorite Dan Coats will defeat Democrat Rep. Brad Ellsworth in a race to replace retiring Democratic Sen. Evan Bayh, and incumbent Sen. Jim DeMint will win another term in South Carolina.
"Tonight, there's a Tea Party tidal wave and we're sending a message to" lawmakers in Washington," Paul said in his victory speech. "It's a message on fiscal sanity, it's a message on limited constitutional government and balanced budgets."
Two of the most high-profile races of the election season, however, appeared to be less favorable for the Tea Party. GOP Delaware candidate Christine O' Donnell, who received the most news coverage of the 2010 candidates, will lose to Democrat Chris Coons, ABC News projections show.
In New York, another controversial race dominated by scandals, Tea Party-backed Carl Paladino is also projected to lose to Democratic Attorney General Andrew Cuomo.
Democrats have so far held on to their Senate seats in California, West Virginia, Hawaii, Maryland, Delaware, New York, Connecticut, Vermont and Oregon. The reigning party will maintain its majority in the Senate but leaders will lose their comfortable hold on the chamber, making it even more difficult to pass legislation on which there is little bipartisan compromise, such as energy and jobs.
Democrats gained a key victory in West Virginia, where Gov. Joe Manchin is projected to win, and in Connecticut, where Richard Blumenthal is projected to defeat World Wrestling Entertainment's Linda McMahon. While 88 percent were worried about the economy in Connecticut, they didn't take it out on the Democrat as voters did elsewhere; he won these voters by 54 to 45 percent.
Preliminary exit polls show strong discontent against President Obama in red states and even a surprising number in his home state of Illinois, where 48 percent disapprove of the president's performance, compared with 51 percent who approve of him. Voters have been hard hit by the economy, with four in 10 saying someone in their household has lost a job or been laid off in the past two years, higher than the three in 10 nationally who say the same.
Obama carried Colorado with 53 percent of the vote in 2008; fewer of voters now, 47 percent, approve of the job he is doing as president.
Older voters have voted for the Democratic candidate in each of the past three Senate races, including voting for Feingold in 2004 by a 14-point margin, but not this time. Those age 65 and older went for Johnson, 54-46 percent.
In Kentucky, 52 percent of voters said Paul's views were too extreme but the libertarian-leaning ophthalmologist won on the back of strong anti-President Obama sentiment in the state. By a 23-point margin, voters there said they were casting their ballots in opposition to Obama, with 62 percent disapproving of Obama's job performance overall, according to ABC News exit polls.
The sentiment was similar in West Virginia, which has voted Republican in the last three presidential elections. Seven in 10 disapprove of Obama's job performance, with approval at 30 percent. Nearly half of West Virginia voters said their vote was to express opposition to Obama, while far fewer -- 14 percent -- said they voted to express support for the president.
"Will the president take a lesson away from tonight?" House Tea Party caucus founder Michele Bachmann said on ABC News Now. "This is a profound repudiation of his policies."
Across the country, Senate incumbents, especially Democrats, were fighting for their political lives today, hoping to withstand Tea Party momentum and an election that has morphed into a referendum on Washington.
Democrats currently hold 59 seats in the Senate, Republicans 41. There were 37 seats in play, and the GOP needed an additional 10 seats to regain control.
In one of the most high-profile and anticipated races of the night, Reid defeated Angle, a Tea Party favorite.
Fifty-five percent of Nevada voters in preliminary exit poll results said they disapprove of the job he is doing in the Senate, and 56 percent said they think the Senate majority leader has been in Washington too long.
At the same time, he won support on other grounds. A narrow majority of voters, 52 percent, said they prefer an insider who knows how to get things done over an outsider "who wants to shake things up." And when it came to picking the one candidate quality that mattered most to them, Nevada's voters were divided: 31 percent said they wanted change, but 29 percent said they were looking for someone who understood their needs, and nearly as many were looking for experience.
Preliminary exit poll results underscored the economic distress defining the 2010 election. Eighty-eight percent of voters today said the national economy's in bad shape, nearly as many as the record 92 percent who said so two years ago. Only 14 percent say their own family's financial situation has improved since 2008.
And few see much respite: Compounding the political impact of the long downturn, 86 percent remain worried about the economy's direction in the next year, including half who are "very" worried.
The economy has deeply affected the broader public mood. Sixty-two percent say the country is seriously headed in the wrong direction (a record 74 percent said so in 2008, as the economy fell into the abyss). More broadly, 39 percent expect life for the next generation of Americans to be worse than it is today, compared with 32 percent who say better.
It's not just the Democrats who are suffering at the hands of the anti-Washington sentiment; even some Republican candidates face an uphill battle.
Sen. Lisa Murkowski, R-Alaska, who has been in the Senate for eight years, is embroiled in a race that has divided the Republican Party. She faces a tight race against Joe Miller, the Tea Party candidate who astonished the Republican establishment by defeating Murkowski in the primary.
In recent weeks, the race between the two has narrowed as Miller faces questions about his past employment history and whether he broke his employer's rules as an attorney at the Fairbanks County Borough.
Amid concern about Miller's standing plummeting in the polls and Democrat Scott McAdams' gaining an edge, Republicans have shifted their allegiance to Murkowski, who was unceremoniously stripped of her post last month in the Senate leadership after she defied party leaders and announced her intention to wage a write-in campaign.
According to Alaska election officials, the write-in Senate candidate, which included Republican Sen. Lisa Murkowski, was leading by 39 percent of the vote, with 27 percent of precincts reporting. first name Miller had 34 percent of the vote and first name McAdams 25 percent.
The Alaska Division of Elections only counts the names of write-in candidates if they exceed THIS wording correct? names on the ballot or if the write-ins are within 0.5 percentage points of the leading candidate.
Officials will count misspelled names that show voter intention, but there are a number of other write-in candidates also on the ballot besides Murkowski.
ABC News' Gary Langer contributed to this report.