Joe Sestak and Rand Paul defeat incumbents with high-level endorsements.
Angry American voters soundly rejected establishment candidates in two state primary elections, reflecting the ever-deepening partisan chasm in U.S. politics.
Battered by the worst economic downturn in at least seven decades and disgusted with the perception that Washington politicians dance to the tune of special interests, voters turned on candidates endorsed by President Barack Obama and Sen. Mitch McConnell, the top Senate Republican.
While primary elections serve only to select party candidates for the general election in November, the outcome of Tuesday's polling foreshadowed an unpredictability that could significantly reshape the U.S. political landscape.
Voters are in a vibrant anti-incumbent, anti-Washington mood and have lost patience with entrenched politicians seen as out of touch with the public, bailing out wealthy bankers while middle-class Americans struggle to keep their jobs and their homes.
In Kentucky, the upstart tea party movement — pressing for lower taxes and smaller government — pushed political novice Rand Paul onto the ballot as the Republican candidate for the Senate, a clear rejection of the wishes of Sen. Mitch McConnell, the top Republican in Washington.
President Barack Obama's backing — although lukewarm toward the end of the primary campaign — failed to help Sen. Arlen Specter, a five-term incumbent who switched from Republican to Democrat last year in hopes of keeping his Pennsylvania seat.
He was overwhelmed by Congressman Joe Sestak, a retired Navy admiral, who defied party leaders in pursuing the nomination.
"This is what democracy looks like," Sestak yelled at supporters Tuesday night. "A win for the people over the establishment, over the status quo, even over Washington, D.C."
In Arkansas, Sen. Blanche Lincoln, a moderate who was first elected in 1998 and is considered among the most vulnerable Senate Democrats this fall, was the top vote-getter. But she failed to win the majority needed to avoid a costly run-off against Lt. Gov. Bill Halter. He had the backing of labor unions and left-of-center progressives.
The winner of the June 8 run-off will face Rep. John Boozman, who won the Republican nomination.
Turnout was better than normal for the primaries in Pennsylvania, Arkansas and Kentucky, suggesting deeper voter anxiety about their futures in an economy with such a slow recovery that national unemployment still hovers near 10 percent.
Five months remain to the November general election, where Obama's Democrats will struggle to preserve their majorities in both houses of Congress. With the most seats to defend, Democrats are most vulnerable to the anti-incumbent sentiment.
But Democrats received an important boost as they won a closely watched special congressional election in Pennsylvania to fill the seat of the late Rep. John Murtha. Though the winner, Mark Critz, will serve only the final months of Murtha's term, a defeat would have been discouraging in a heavily working-class district held by Democrats for four decades.
In Kentucky, the Paul victory demonstrated the political power of the tea party movement, which believes that government spending and influence should be curbed. It already had helped prevent a Republican senator from Utah, Bob Bennett, from gaining re-nomination for his seat because he was seen as insufficiently conservative.
"I have a message, a message from the tea party, a message that is loud and clear and does not mince words: We have come to take our government back," Paul said.
While his rival had the backing of the Republican establishment, Paul, an eye surgeon and the son of former presidential candidate, libertarian-leaning U.S. Rep. Ron Paul, had the support of some key conservatives, including former vice presidential candidate Sarah Palin.
Palin told The Associated Press in a telephone interview that Paul's victory is a "wake up call for the country."
Paul had 59 percent of the vote to 35 percent for Grayson. He will face state Attorney General Jack Conway, who won the Democratic nomination Tuesday.
Conway, 40, used his victory speech to try to portray Paul as outside the mainstream.
"We have a fundamental decision to make in this most important of Senate races," Conway said. "Are we going to use that passion to heat the building? Or are we going to use that passion to burn it down?"
Specter's defeat signals the weakening of the American political center. He quit the Republican Party when he believed he had little hope of fending off a primary challenge from Pat Toomey, a more conservative former congressman. Toomey won his party's nomination Tuesday.
Yet Specter also was not liberal enough to win the Democratic nomination, despite Obama's support. Sestak accused Specter of switching parties to save his job and said Specter could not be trusted to support Democratic Party values. Sestak's campaign ran television commercials from the 2004 Senate campaign that showed former President George W. Bush saying he could count on Specter, then a Republican.
Sestak, at 58, also projected relative youth compared with the 80-year-old Specter.
Sestak received 54 percent of the vote; Specter had about 46 percent.