JACKSON, MISS. — Chris McDaniel supporters vowed to keep up the fight after the primary runoff was called for Sen. Thad Cochran Tuesday night, but by Wednesday afternoon several outside groups and one prominent Mississippi Republican threw cold water on talk of an official challenge. “My understanding is that is not going to happen,” said Sen. Roger Wicker (R-Miss.) from Washington. “I kind of heard it through the grapevine at lunch.” Wicker supported Cochran’s reelection and was intimately involved in his fundraising operation for the runoff. The Club for Growth and Senate Conservatives Fund — two of McDaniel’s biggest national...