Tea Party challenger Chris McDaniel forces runoff vs. MS GOP Sen. Thad Cochran

Sen. Thad Cochran of Mississippi and Tea Party challenger Chris McDaniel battled to a virtual draw on Tuesday in their bitter Republican Senate primary and appeared headed to a rematch in a June 24 runoff.

Neither candidate appeared likely to capture the 50 percent of the vote needed for a clear win. With about 98 percent of the votes counted, McDaniel had 49.6 percent and Cochran 48.8 percent -- a difference of about 2,500 votes.

A little known third candidate, Thomas Carey, drew about 1.6 percent of the vote, keeping the leaders short of the 50 percent mark.

The divided result likely means three more weeks of heavy spending and bitter accusations in a primary race dominated in the final days by a controversy involving a local blogger who snuck into a nursing home to photograph Cochran's bedridden wife, who suffers from dementia.

McDaniel's campaign denied any involvement, but four of his supporters face criminal charges in the incident and the two campaigns traded accusations of dirty politics.

The Mississippi contest, along with a Republican Senate primary in Iowa, highlighted a busy day of voting across the country as eight states held primaries to select nominees for the Nov. 4 midterm elections.

Republicans must pick up six seats to gain a U.S. Senate majority, and the Iowa and Mississippi races could be crucial to their effort.

Cochran, 76, had hoped to extend a string of Senate primary victories -- in Texas, Kentucky, North Carolina and Oregon -- by the Republican establishment against the insurgent Tea Party movement. The Mississippi race was seen as the Tea Party's best chance to knock off a sitting senator this year.

During the primary campaign, Cochran, a six-term senator, stressed the power of incumbency and his ability to deliver money and benefits to Mississippi. McDaniel, a 41-year-old state senator, had argued Cochran was not conservative enough and the state needed new blood in Washington.

Democrats hope their nominee, former U.S. Representative Travis Childers, faces the deeply conservative McDaniel, who they see as vulnerable enough to potentially make the race competitive. Democrats have not won a Senate race in Mississippi since 1982.

Outside conservative groups like the anti-tax Club for Growth and Senate Conservatives Fund spent millions during the primary to help McDaniel, who also gained endorsements from Tea Party favorites such as former Alaska Governor Sarah Palin.

The other states voting on Tuesday were Iowa, Alabama, California, Montana, New Jersey, New Mexico and South Dakota.

In Iowa, targeted by Republicans as a prime takeover opportunity after the retirement of Democratic Senator Tom Harkin, state senator Joni Ernst easily beat four other candidates to win the nomination to face Democratic U.S. Representative Bruce Braley.

Ernst, who gained national attention for an ad featuring her experience at hog castration, had won support from both ends of the Republican ideological spectrum, picking up endorsements from Palin and from business-friendly 2012 Republican presidential nominee Mitt Romney.