WASHINGTON (AP) — Locked in a squeaker of a race, Mississippi Sen. Thad Cochran and tea party-backed challenger Chris McDaniel pointed toward a possible June 24 runoff after battling to a near-draw Tuesday in a primary that underscored Republican differences.

Unofficial returns from 99 percent of the state’s precincts showed McDaniel with slightly under 50 percent of the vote in a three-way race and Cochran slightly under 49 percent. It takes a majority by one candidate to avoid a runoff.

“For too long, we’ve been silent. For too long, we sat still. For too long, we let them have their way with us,” McDaniel told supporters late Tuesday in a slap at the Washington establishment.

“It’s looking like a runoff,” conceded Rep. Gregg Harper, addressing a crowd of Cochran supporters.

The Mississippi contest easily overshadowed races in seven other states, several of which sent GOP establishment-backed candidates into fall campaigns for Senate seats that Republicans have targeted in their drive to gain six seats and a majority.

State Sen. Joni Ernst overwhelmed her rivals in Iowa, easily surpassing the 35 percent total needed to win the nomination outright. She will take on Democratic Rep. Bruce Braley this fall for a Senate seat long in Democratic hands.

In South Dakota, former Gov. Mike Rounds won the Republican nomination and quickly became a favorite to win a seat held by retiring Democratic Sen. Tim Johnson. Rick Weiland is the Democratic candidate in the heavily Republican state.

And in Montana, appointed Democratic Sen. John Walsh and Republican Rep. Steve Daines won nominations en route to a fall campaign that the GOP is expected to target as an opportunity to gain a seat.

Mississippi officials said the vote tally did not include provisional ballots, some of them cast as a result of the state’s new voter ID law. Those voters have five days to furnish proof of residence. An official canvass could take longer, until June 13.

The contest was a race between a pillar of the GOP establishment who has helped funnel millions of dollars to his state and a younger state lawmaker who drew backing from tea party groups and former Republican vice presidential candidate Sarah Palin. The incumbent stressed his seniority and proven ability to help Mississippi, while his challenger called for term limits and a balanced budget amendment to the Constitution.

The campaign took a turn toward the sensational when four men, all McDaniel supporters, were arrested and charged with surreptitiously taking photographs of Cochran’s 72-year-old wife, who suffers from dementia and has long lived in a nursing home.

The race was arguably the year’s last good chance for the tea party wing of the GOP to topple an establishment favorite in a Senate primary, following losses in Texas, North Carolina, Georgia and Kentucky.

Early Wednesday, outside anti-establishment groups pledged to continue the fight. The anti-tax Club for Growth urged Cochran to end his bid for re-election and threatened to continue what has already been a $2.5 million campaign against him. The activist-focused FreedomWorks for America also vowed to stand with McDaniel through a runoff.

“Grassroots shows up when it counts,” FreedomWorks chief Matt Kibbe said.

Already, outside groups have poured more than $8 million into the race, with McDaniel enjoying a 2-to-1 tilt in his favor.

The stakes in the overall struggle for control of the Senate loomed larger in Iowa, where Democratic Sen. Tom Harkin’s retirement created an open seat that Democrat Braley, a fourth-term lawmaker, seeks to fill — as does Ernst.

She fashioned her rise in the race on memorable television commercials.

Republicans eyed another fall pickup opportunity in South Dakota, where Democratic Sen. Tim Johnson is retiring and Rounds easily eclipsed his rivals for the GOP nomination. Rick Weiland, making his third try for a seat in Congress, was unopposed by other Democrats.

Democratic Sens. Tom Udall in New Mexico and Cory Booker in New Jersey also were nominated for new terms, and head into the fall as favorites.

In gubernatorial primaries, Gov. Jerry Brown of California won the Democratic nomination to a fourth term. Republican governors winning renomination included Robert Bentley in Alabama, Dennis Daugaard in South Dakota and Terry Branstad in Iowa. Gov. Susana Martinez had no Republican primary opposition in her pursuit of a second term in New Mexico.