Sen. Thad Cochran (R) is likely facing a runoff in Mississippi. (AP Photo/Rogelio V. Solis)

The U.S. Chamber of Commerce and a super PAC backing Sen. Thad Cochran (R-Miss.) each vowed to keep supporting the senator in his reelection bid in the likely case that he advances to a runoff against tea party-backed state Sen. Chris McDaniel.

"We're not running away from Sen. Cochran," the Chamber's political director, Rob Engstrom, told Post Politics. "We're going to continue to stand by him." The Chamber spent $500,000 hitting McDaniel leading up to Tuesday's primary, according to the Sunlight Foundation's tally.

Mississippi Conservatives, a super PAC that was designed specifically to boost Cochran and that became his biggest spending ally in the primary, said it, too, would be there for the senator.

"We're going to be heavily engaged in this race," said Henry Barbour, who heads up the group. "We think Mississippi's interests are at stake. We are going to put Mississippi's interests first."

Neither Mississippi Conservatives nor the chamber said how much it was willing to spend to help Cochran in what would be a three-week sprint to the finish. With more than 99 percent of precincts reporting, McDaniel (49.5 percent) led Cochran (48.9 percent)  by less than one percentage point. If the numbers hold, there will be a June 24 runoff, since no candidate will have claimed a majority.

Tea party groups vowed to redouble their efforts Wednesday. One of them, the antitax Club for Growth, called on Cochran to bow out. Barbour slammed the Club for suggesting the idea.

"Those groups like the Club For Growth that think they can just ignore the will of Mississippi voters and not have a runoff -- how obnoxious is that?" he asked.