WASHINGTON (AP) — The tea party wing of the Republican Party has a chance to regain some of its luster when a challenger from the conservative, anti-tax faction faces a veteran Republican incumbent in a U.S. Senate primary runoff in Mississippi.

Unofficial results showed tea party challenger Chris McDaniel with a slight lead Wednesday over six-term incumbent Thad Cochran in the three-way race. Most precincts have reported and an unknown number of mail-in and provisional ballots have yet to be counted.

Neither McDaniel nor Cochran received a majority of the vote, which would have been needed to avoid the runoff scheduled in three weeks.

If McDaniel wins, it would provide a boost to the tea party. However, it's not likely to affect the battle for control of the Senate. The winner of the Democratic nomination, former Rep. Travis Childers, is unlikely to defeat either McDaniel or Cochran in this staunchly conservative state that last elected a Democratic senator in 1982.

The anti-tax, small-government tea party rose to prominence after the 2008 election of President Barack Obama, and the movement helped the Republicans capture the House two years later.

But after the Republicans failed to take back the Senate in 2012, some of the tea party faction's luster has faded. Tea party-backed challengers this year failed to topple high-profile Republicans in Senate primaries in Texas, Georgia, North Carolina and Kentucky.

Establishment-backed Republican candidates prevailed in other key primary races around the country Tuesday, as the party leadership continued its mostly successful effort to put mainstream candidates on the ballot in the November general elections.

Hoping to pick up six seats need to capture the Senate majority, the Republican Party leadership is concerned that general election voters will be put off by the most extreme of the tea partiers.

The party's big majority in the House of Representatives is not in danger. If it takes control of both houses of Congress it would likely kill any chance Obama has of moving his legislative agenda in the final two years of his term.

The contest between Cochran, 76, and McDaniel, 41, was a costly and heated race between a pillar of the Republican establishment who has helped funnel millions of dollars to his state and cast himself as a reliable opponent of Obama and a younger state lawmaker who criticized the incumbent for being too willing to go along with Democrats in Washington.

The campaign took a sensational turn when four McDaniel supporters were arrested and charged with surreptitiously taking photographs of the senator's 72-year-old wife, who suffers from dementia and has long lived in a nursing home. McDaniel said he knew nothing about it, but Cochran supporters suspected dirty politics.

Eight states in all held primaries Tuesday.