"My long time friend, Mike Rounds, is exactly what we need in the United States Senate,” Huckabee said in a statement.

“His experience as governor of the great state of South Dakota, dedication to tackling the federal debt, strengthening and honoring our military, border security, as well as his strong support of faith, family, life and freedom — makes my endorsement a great pleasure.”

Huckabee is host of a conservative talk-radio show, and his endorsement of Rounds, who has received criticism from activists on the right in South Dakota, is likely to boost him in case of a primary fight.

Rep. Kristi Noem (R-S.D.) has been suggested as a potential conservative challenger to Rounds, and she hasn't yet ruled it out.

Democrats have yet to front a candidate for retiring Sen. Tim JohnsonTimothy (Tim) Peter JohnsonSeveral hurt when truck runs into minimum wage protesters in Michigan Senate GOP rejects Trump’s call to go big on gun legislation Court ruling could be game changer for Dems in Nevada MORE's (D) seat, but two prominent South Dakota Democrats — former Rep. Stephanie Herseth Sandlin and Attorney General Brendan Johnson, the senator's son — are both considering running.