Republican Sen. Bob Bennett of Utah and Republican-turned-Democrat Sen. Arlen Specter of Pennsylvania already have lost their re-election bids.
The centrist Lincoln, a two-term senator, is in a runoff against Arkansas Lt. Gov. Bill Halter, who is being supported by labor unions and liberal groups that have spent millions to try to unseat the White House-backed senator. They were forced into a runoff for the party nomination after neither captured 50 percent of the vote in the May 18 primary.
The anti-incumbent mood also has put the vulnerable Senate Majority Leader Harry Reid of Nevada and liberal stalwart Sen. Barbara Boxer of California on notice that they'll face tough re-election fights regardless of who the Republicans nominate.
In Nevada, three Republicans are in a bruising fight for the chance to take on Reid in November. Sharron Angle, a favorite of the grassroots conservative tea party movement, had an edge in final polling. Angle wants to abolish the federal income tax code and phase out Social Security for younger workers — policies which Reid supporters depict as too extreme for most Nevadans.
In California, former Hewlett Packard Co. chief executive Carly Fiorina, who has former Alaska Gov. Sarah Palin's support, was leading the three-candidate field for the chance to challenge Boxer.
California also hosts a marquee Republican primary in the race to succeed term-limited Gov. Arnold Schwarzenegger.
Republican billionaire Meg Whitman, a former eBay chief executive who has spent more than $70 million of her own fortune, faced state insurance commissioner Steve Poizner, a wealthy former businessman. Attorney General Jerry Brown, a former governor, is the likely Democratic nominee.
On the busiest night thus far of this year's election calendar, voters were choosing Democratic and Republican nominees for governor in several other states like Iowa, where the general election contest was certain to be competitive. Republican primary voters in South Carolina were settling a nasty four-way gubernatorial primary contest.
The outcomes will determine matchups for November, when Democrats will try to maintain their comfortable majorities in the House and Senate and overcome Republican challenges in dozens of gubernatorial races.
Historically, the party that controls the White House takes a beating in the president's first midterm elections.
Still, neither party was safe from voters' ire.
Nationwide, Democrats and Republicans alike were facing an electorate angry over everything from the persistent economic woes to the typical ways of Washington.
A Pew Research Center poll in April found that public confidence in government was at one of the lowest points in a half century. And earlier primaries indicated that voters are willing to fire Washington incumbents — regardless of party.
In South Carolina, six-term Republican Rep. Bob Inglis was trying to fend off primary challengers who have made the race a referendum on his 2008 vote to bail out the nation's banking industry.
Republicans appear ready to oust Nevada Gov. Jim Gibbons in the wake of his messy divorce; former federal judge Brian Sandoval is favored for the Republican nomination.
Elsewhere, South Carolina Republicans were choosing a successor for the term-limited and scandal-scarred Republican Gov. Mark Sanford, and the victor likely will become governor of the heavily Republican state.
State Rep. Nikki Haley had the advantage in the final days; she is trying to become the state's first female governor and overcome allegations of infidelity, which she denies. She has also been the target of racial slurs because her parents are Sikhs who emigrated from India.
In Iowa, three Republicans are battling for the right to oppose Democrat Chet Culver, considered one of the nation's most vulnerable governors.
Georgia. Maine, Montana, New Jersey, North Dakota, South Dakota and Virginia also hold primaries.
