McDaniel had been floating a primary challenge to either Cochran or Rep. Steven Palazzo (R-MS) prior to his announcement.
Tea Party groups in the state support McDaniel and within minutes the Senate Conservatives Fund, Club for Growth, and Madison Project offered their endorsements.
"Chris McDaniel is a constitutional conservative who will fight to stop Obamacare, balance the budget, and get America working again," Senate Conservatives Fund Executive Director Matt Hoskins said in a statement . "Chris McDaniel is not part of the Washington establishment and he has the courage to stand up to the big spenders in both parties. He's a principled leader who will make Mississippi proud."
Cochran has not officially announced whether he is running for reelection.