Add Mississippi's Thad Cochran to the list of Republican Senators up for re-election next year who are facing primary challengers.
State Senator Chris McDaniel launched a campaign on Thursday to try to unseat Cochran, who's served in Congress for more than four decades.
Cochran, who hasn't announced yet whether he'll run in 2014 for a seventh term in the Senate, voted Wednesday night in favor of the agreement to end the partial federal government shutdown and extend the nation's debt ceiling.
And that vote wasn't lost on McDaniel, a two-term state senator with close ties to tea party activists and other grassroots conservatives.
"There are those in D.C. that don't appear to be listening. There are those in D.C. that don't appear to care for the Constitution," said McDaniel in web video. "We stand today ready to restore the Constitution. We stand today ready to restore this Republic. But, it will take action. It will take people across this state ready to make an aggressive move to do the right thing."
An e-mail from McDaniel's campaign includes endorsements from nine fellow state senators. Senate Conservatives Fund and Club for Growth, two DC based groups that have a history of backing conservative primary challengers, immediately endorsed McDaniel.
If Cochran does decide to run for re-election, he would become the fifth Republican Senator facing a primary challenge, joining Majority Leader Mitch McConnell of Kentucky, Lamar Alexander of Tennessee, Lindsey Graham of South Carolina, and Mike Enzi of Wyoming.