WASHINGTON (AP) — Former presidential contender Rick Santorum and vice presidential nominee Sarah Palin on Thursday began star turns in ads backing the Mississippi state lawmaker challenging longtime Republican Sen. Thad Cochran in next week’s Senate primary.

Santorum and Palin were the latest conservative darlings to back Chris McDaniel, whose challenge to Cochran is poised to be one of the few potential success stories for the tea party this election year. Outside groups have poured millions into the race, which illustrates the split within the GOP between rank-and-file activists and establishment-minded operatives and donors.