JACKSON, Mississippi (CNN) -- The Mississippi race between longtime Sen. Thad Cochran and conservative challenger Chris McDaniel was too close to call early Wednesday.
Both candidates appeared to be short of the 50% threshold needed to avoid a runoff, making it hard to project a clear winner.
If the numbers hold up and and no candidate gets more than half of the vote, Cochran and McDaniel will have a runoff on June 24.
The Mississippi race is a high-profile tea party vs. mainstream showdown. For tea party supporters, it's perhaps their best chance to claim victory after facing a string of defeats this year.
Tuesday marked the biggest single day of primary voting this year, with eight states holding contests from coast to coast.
In Iowa, the winner of the GOP Senate primary had rare support from both sides of the GOP battle between conservatives and the establishment. If Republicans can flip the Hawkeye State and five other Democratic-held seats, they will regain control of the Senate.
And California used its new "jungle" primary system for the first time in a gubernatorial race, where the top two finishers advance to the November election, regardless of party affiliation. Results are still trickling in for other key races.
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At 76, Cochran is the second-oldest Senate incumbent running for re-election this year. McDaniel ran on a platform of change, saying Cochran, who has served in Congress for four decades, has been in Washington long enough.
"We don't have six more years of the status quo," he recently told CNN. "I am not going to Washington D.C. to be a member of the cocktail circuit or to make backroom deals. I'm going up there to fight and defend the Constitution."
While Cochran didn't speak at his election night headquarters Tuesday night, McDaniel came out on stage at his own party and told the crowd the results should be firm by Wednesday.
"But one way or the other I promise you this, whether it's tomorrow or whether it's three weeks from tonight, we will stand victorious in this race," he said.
Cochran has been widely considered the most vulnerable GOP senator facing re-election. But momentum seemed to shift after McDaniel's campaign was recently put on defense over a bizarre scandal involving people who support him.
A political blogger was arrested last month after taking a picture of Cochran's ailing wife in her nursing home bed. Three other McDaniel supporters were later arrested in connection with the stunt.
While McDaniel's campaign has forcefully condemned the act and denied having any involvement or knowledge of the plot, that didn't stop Cochran's campaign from trying to link the controversy to McDaniel in an attack ad. The incident was the latest salvo in what turned into an ugly primary fight.
McDaniel was backed by many national anti-establishment and tea party groups. The Senate Conservatives Fund and the Club for Growth, two Washington-based groups that often back conservative candidates who launch primary challenges against incumbent Republican senators, both spent big bucks to run television commercials supporting McDaniel and criticizing Cochran.
McDaniel also grabbed support from the political wings of the Tea Party Express, the Tea Party Patriots and FreedomWorks, and was joined on the campaign trail the weekend before the primary by two rock stars on the right, former Alaska Gov. Sarah Palin and former Sen. Rick Santorum of Pennsylvania, a 2012 GOP presidential candidate who's seriously considering another run for the White House.
Former Mississippi Gov. Haley Barbour blasted McDaniel for bringing in "outside celebrities," describing the race as "out-of-state money, celebrities and political gunslingers versus leaders who live here, love the state and want to do what is best for Mississippi."
The Barbour-backed Mississippi Conservatives PAC dished out six figures to support Cochran, who was also backed by the U.S. Chamber of Commerce.
While Cochran outraised and outspent McDaniel, the flood of outside money in the race evened things out between the two candidates.
The winner will face off against former Rep. Travis Childers, who CNN projects will be the Democratic nominee, in November.
State Sen. Joni Ernst didn't have to take sides in the battle between grass-roots conservatives and the Republican establishment: She had the backing of both--and easily came out on top in a crowded, five-way primary race.
Ernst, a lieutenant colonel in the Iowa National Guard who grabbed national attention earlier this year by touting her hog castrating skills in a campaign commercial, had the support of some top names and groups among both the tea party movement and the mainstream GOP.
At her victory party Tuesday night, Ernst acknowledged and thanked her GOP competitors.
"It is going to take all of us pulling together to unite this party and win in November," she said.
Ernst will face off against Democratic Rep. Bruce Braley. The winner of November's general
election will succeed longtime Democratic Sen. Tom Harkin, who is retiring at the end of the year.
Republicans believe they have a good shot at flipping Harkin's seat in their drive to retake the Senate.
Big name Republicans from both the establishment and conservative wings of the party like Mitt Romney, Marco Rubio and Sarah Palin have joined Ernst on the trail. She's gotten support from establishment groups like the Chamber of Commerce as well groups like the Senate Conservatives Fund, which often backs conservative candidates who launch primary challenges against incumbent Republican senators.
California gubernatorial race:
CNN Projects that Democratic Gov. Jerry Brown and Republican Neel Kashkari have finished in first and second place, respectively, and will advance to the general election in November.
For the first time in statewide races, California held "open" or "jungle" primaries, in which all candidates compete in a single contest and the first and second place finishers, regardless of party affiliation, advance to the general election.
Kashkari was vying with Tim Donnelly for the second spot. Both are Republicans.
Some GOP strategists said they're concerned that if it's Donnelly, a conservative with tea party backing, it could hurt Republican candidates in down-ballot races in a state where the general election electorate is much more moderate than that of the GOP primary.
But wait, there's more.
One time anti-war protester Cindy Sheehan is also on the ballot, the nominee of the Peace and Freedom Party, a socialist party whose gubernatorial candidates have traditionally grabbed about 1% of the vote.
Sheehan became the face of the anti-Iraq war movement in 2005 when she protested for weeks outside then-President George W. Bush's ranch in Crawford, Texas, after her son Casey was killed in combat.
California 33rd Congressional District:
A self-help guru. A public radio host. A sports executive. A television producer.
Those are just four of the 16 candidates running in the primary for California's 33rd Congressional District, which includes Hollywood.
The district also contains parts of Westside Los Angeles, as well as the opulent cities of Beverly Hills, Bel Air and Brentwood. The area is losing its longtime congressman, Democrat Henry Waxman, who announced earlier this year he would retire at the end of his 20th term.
Keeping up with the celebrity endorsements and the money race in this part of the state can be a challenge. Marianne Williamson, the self-help guru, has the backing of Katy Perry and Kim Kardashian, for example.
Los Angeles City Controller Wendy Greuel and state Sen. Ted Lieu, both Democrats, are considered the most likely candidates to place in the top two and advance to the general election.
But with just as many Republicans and independents as Democrats running for the seat -- and an expected low turnout -- it's possible the race may not end up as an intra-party fight.
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