Donald Trump’s endorsed candidate struggles as old and new Republican parties clash in Alabama Senate race

Rep. Mo Brooks leaves little doubt about how he hopes to win the Republican primary for Alabama’s open U.S. Senate seat next year. The words “Endorsed by Trump” precede his name in his campaign logo, and the same message is printed in his Twitter handle.

But eight months after receiving the former president’s highest blessing in one of the nation’s reddest states, Brooks is still struggling to win Trump’s approval behind the scenes, and his standing has begun to fade in the state amid fierce competition.

As a result, Alabama is once...