The slogan “Remember Mississippi” has become shorthand around here for the unshakable belief among conservative activists that Senator Thad Cochran occupies a stolen seat…

If Mr. McDaniel runs, as expected, he will face Senator Roger Wicker in a primary in June — the first election next year in which Republican Senate candidates would square off. The race could offer an early answer to a question that is vital to the party’s future: Does the effort to replace sitting Republicans with populist conservatives in the mold of Mr. Trump have a credible chance of maturing into the national movement its backers envision as they plot a course across the South and then westward to states like Nevada, Arizona, Nebraska, Wyoming and Utah?…

“We sensed the anger in ’13 and ’14,” Mr. McDaniel said in an interview at his law practice in downtown Laurel. “That anger,” he added, “reached its apex, it seemed, with Trump’s election. But now that McConnell and his merry band of yes men like Wicker have stood in the way of Trump, that anger has escalated again.”