JACKSON, Miss. — Forced into a Mississippi runoff, challenger Chris McDaniel and veteran Sen. Thad Cochran plunged into a three-week campaign Wednesday as voters prepare to pick a Republican candidate for the fall and settle the tea party's last, best attempt of the year to topple a pillar of the establishment.

McDaniel, a narrow leader in the vote tally, spent the day resting with his family and "gearing up for what will hopefully be three more weeks of vigorous debate on the important issues facing Mississippians," said spokesman Noel Fritsch.

Cochran, seeking a seventh term, skipped votes in the Senate during the day. He and his allies sought to put the best face on a relatively weak showing at the ballot box after three decades in office spent directing federal funds to his economically distressed state.

"We had a great day yesterday, and it is one more step toward making November Mississippi's moment when we take back the U.S. Senate," Cochran said in a written statement.

Yet there were indications of concern among supporters of the 76-year-old Senate veteran. Asked about Cochran's prospects, fellow Mississippi Republican Sen. Roger Wicker paused at length before responding: "What do you think?" He then predicted Cochran's victory in the runoff.

The third candidate in the race, real estate agent Tom Carey, said in an interview that he had a preference between Cochran and McDaniel but declined to disclose it.

"The two candidates need to talk about issues instead of the backbiting and backstabbing that they've done," Carey said, referring to the controversy that came when four supporters of McDaniel were arrested and charged in an alleged plot to illegally photograph Cochran's wife, who has dementia and lives in a nursing home.

Results from 99 percent of the state's precincts showed McDaniel with 155,040 votes, or 49.5 percent. Cochran had 153,654, or 49 percent. Carey had 4,789 votes, or 1.5 percent, a sliver of support but enough to prevent either of the other two from reaching the needed majority.