Katie Britt defeats Mo Brooks in Alabama’s Senate runoff.

Katie Britt, a former lobbyist and chief of staff to Senator Richard Shelby, has defeated Representative Mo Brooks in a runoff for the Republican nomination in the open Senate race in Alabama, according to The Associated Press.

Ms. Britt, 40, a first-time candidate, had the support of the Republican establishment, Mr. Shelby and several outside groups that shelled out millions to bolster her campaign. In Republican-dominated Alabama, Ms. Britt is now heavily favored to win the seat Mr. Shelby, who is retiring, has held since 1987.

The primary had initially promised to be a showdown between the party’s old guard and its insurgent Trump wing. But the clash never quite materialized. Mr. Brooks, a conservative firebrand who embraced falsehoods about the 2020 presidential election, was lifted by an early endorsement from former President Donald J. Trump, only to see Mr. Trump pull his support as Mr. Brooks’s campaign flagged.

Ms. Britt raised nearly twice as much money as her runoff opponent and saturated the Alabama news media with her message throughout the primary season. Her campaign spent more than $4 million on advertisements, according to the advertising data tracker AdImpact.

In the race’s final days, her ads carried an “Alabama First” slogan, echoing Mr. Trump’s rallying cry, and focused on base-pleasing talking points on border security, abortion and inflation.

Ms. Britt nearly avoided a runoff in the May 24 primary election, garnering 45 percent of the vote and finishing well ahead of Mr. Brooks, who trailed her by more than 15 points. But her campaign’s biggest boost came in its final weeks, when Mr. Trump threw his support her way.

In his statement announcing his endorsement, Mr. Trump called Ms. Britt “a fearless America First Warrior,” trying to burnish her credentials with the Trump-aligned wing of the party. He also railed against Mr. Brooks, noting that the congressman, who fired up protesters before the Capitol attack on Jan. 6, had since told his supporters it was time to put the 2020 election “behind you.”

Mr. Trump pulled his endorsement several months after that, when Mr. Brooks’s standing in the polls began to lag, and accused him of “going woke.”

Mr. Brooks responded to the former president’s condemnation with criticisms of his own, telling Al.com last week, “It’s quite clear that Donald Trump has no loyalty to anyone or anything but himself.”

Ms. Britt will face Will Boyd, a Democratic pastor from northern Alabama, in November.