Veteran Mississippi Sen. Thad Cochran squeaked by challenger Chris McDaniel on Tuesday in a bitterly contested Republican runoff that likely represented the Tea Party's best remaining chance to take down a longtime incumbent.
With 99 percent of precincts reporting, The Associated Press called it for Cochran, who had 51 percent to McDaniel's 49 percent.
Five other states Colorado, Maryland, New York, Oklahoma and Utah held primaries Tuesday, and another, South Carolina, had runoff elections, but the marquee race was the Cochran-McDaniel showdown.
McDaniel appeared to have the advantage in the run-up to Tuesday's contest. He narrowly led Cochran in the June 3 primary, was ahead in several post-primary polls and was thought to have momentum against the 76-year-old incumbent.
McDaniel, who hit hard on anti-incumbent and anti-Washington themes, carried national Tea Party support and also had the backing of a range of grass-roots conservative luminaries ranging from Sarah Palin to Rick Santorum to Phyllis Schlafly.
Conservative groups, including FreedomWorks, the Club for Growth and the Senate Conservatives Fund, poured in millions of dollars in outside spending on his behalf.
Cochran, meanwhile, had financial backing from groups including the U.S. Chamber of Commerce and the National Rifle Association. And much of the Mississippi GOP establishment including Gov. Phil Bryant and former Gov. Haley Barbour lined up behind him as well.
National Republicans feared that, in a general election, McDaniel was susceptible to being painted as an out-of-the-mainstream candidate a risky nominee who might put an otherwise safely Republican Senate seat in play.
In the three-week runoff sprint, the six-term incumbent managed to draw on a coalition that included African-American Democrats and independents. Under Mississippi law, Democrats who did not vote in the June 3 Democratic primary could vote in the Republican runoff and they were essential to Cochran's post-primary strategy.
The role Democrats played in lifting Cochran to victory was a point of angry contention Tuesday night: McDaniel refused to concede and made reference to "dozens of irregularities reported across this state."
"There is something a bit strange, there is something a bit unusual, about a Republican primary that's decided by liberal Democrats," he told supporters. "Before this race ends, we have to be absolutely certain that the Republican primary was won by Republican voters."
In November, Cochran will go up against Democratic nominee Travis Childers, a former congressman. Childers faces long odds against the Republican incumbent in conservative Mississippi: Since first winning the Senate seat in 1978, Cochran has never been re-elected with less than 61 percent of the vote.
In Mississippi and elsewhere, it was a great night for incumbents.
In the most closely watched U.S. House race, longtime New York Democratic Rep. Charles Rangel led state Sen. Adriano Espaillat, 47 percent to 44 percent, with 96 percent of precincts reporting.
Espaillat refused to concede on Tuesday night, telling supporters the race was still too close to call.
GOP Rep. Richard Hanna, who represents an Upstate New York district that includes Utica and Binghampton, fended a challenge on his right flank from conservative state Assemblywoman Claudia Tenney. Hanna defeated Tenney, 53 percent to 47 percent, in a primary that drew roughly twice as many voters as in 2012.
In another Senate race that drew national notice, GOP Rep. James Lankford won the special Senate primary to succeed Tom Coburn, who is retiring at the end of the year. By winning 56 percent to former Oklahoma state House Speaker T.W. Shannon's 36 percent, Lankford won the nomination outright and is expected to cruise to victory in November in the solidly Republican state.
In Maryland, Lt. Gov. Anthony Brown won the Democratic nomination for governor, positioning him as the front-runner to succeed outgoing Gov. Martin O'Malley in the solidly Democratic state. If Brown wins in November, he would become the nation's fifth African-American governor.
In Colorado, former U.S. Rep. Bob Beauprez won a four-way GOP primary for governor, running ahead of Tom Tancredo, another former congressman who ran for president in 2008. Tancredo's second-place finish was welcomed by the state Republican establishment many in the party feared that Tancredo, an immigration hard-liner who ran for governor as a third-party candidate in 2010, would prove to be a polarizing nominee who might damage the campaigns of other GOP statewide candidates.