Former President Donald Trump is appearing in a radio ad for U.S. Rep Mo Brooks as he tries to sway the outcome of the state’s Senate race.

Brooks’ campaign said the ad began airing Friday.

“Hi Alabama, this is your favorite president, Donald Trump. Few Republicans have as much courage and fight as Alabama Congressman Mo Brooks. A friend of mine,” Trump says in the ad.

Trump has endorsed Brooks in the GOP primary for the U.S. Senate seat being vacated by Sen. Richard Shelby.

Brooks is in what is expected to be a hard-fought battle for the Republican nomination. He is facing Katie Britt, the former president of the Business Council of Alabama and Shelby’s former chief of staff, and Lynda Blanchard, a businesswoman who was Trump’s ambassador to Slovenia.

Shelby, one of the Senate’s most senior members, announced earlier this year that he would not seek reelection in 2022, igniting what is expected to be a messy GOP primary for the rare open seat.

Brooks was fiercely criticized for telling a rally preceding the Jan. 6 Capitol riot that it was time to “start taking down names and kicking ass.” Brooks said the phrase was intended to fire up the crowd for the next election cycle and is being misconstrued as advocating the violence that ensued.