Former Arkansas Gov. Mike Huckabee on Friday endorsed Sen. Lamar Alexander’s re-election bid in a new campaign ad, saying he is ready to step into the ring and fight against anyone who challenges the veteran lawmaker’s conservative credentials.

“He’s been your governor, university president, America’s secretary of education. He brought the automobile industry to Tennessee. Lamar Alexander is now a remarkable senator that Tennessee needs to return to office,” Mr. Huckabeesays in the 30-second ad. “Oh, and for anyone who wants to pick a fight with for supposedly not being conservative enough, well, you might want to pick a fight with me first.”

The announcement comes a day after former House Speaker Newt Gingrich threw his support behind Mr. Alexander, who is being challenged by state Rep. Joe Carr in the Aug. 7 primary.