“Slowly but surely, conservatives are figuring out I’m the only conservative in this race,” Mr. Brooks said in an interview. He called Mr. Durant “a John McCain-type of Republican” and Ms. Britt “a Mitch McConnell-establishment, open-borders, cheap-foreign-labor, special-interest-group Republican.”

A poker-faced former prosecutor, Mr. Brooks nonetheless seemed to savor, at a couple of campaign appearances on Friday, his comeback from March, when he was polling in the teens and Mr. Trump abandoned him. The former president accused Mr. Brooks of having gone “woke” because he had urged a crowd, months earlier, to put the 2020 election “behind you.”…

In particular, opinions of Mr. Durant and Ms. Britt, who as first-time candidates are less well-known, have been battered by assaults over the airwaves.

The anti-tax Club for Growth, which supports Mr. Brooks, has spent $6 million in the state on ads, including one barraging Ms. Britt — the former head of an Alabama business group — as “really a lobbyist” who supported a state gas tax increase. One ad flashes a tweet from Donald Trump Jr. in 2021 — back when his father still liked Mr. Brooks — calling Ms. Britt “the Alabama Liz Cheney.”