Mike Collins

Derek Dooley campaigned in rural Georgia this month with a lifelong friend: Gov. Brian Kemp, who also happens to be the state’s most popular Republican. Yet Mr. Dooley remains, by his own admission, the underdog in the Republican Senate primary runoff.

His opponent, Representative Mike Collins, who led after both advanced to a runoff in the first-round election last month, is the race’s self-styled MAGA candidate. President Trump has not endorsed either man ahead of the June 16 runoff — at least not yet.

But Mr. Collins told a Republican women’s club in suburban Griffin last week that Georgia’s MAGA crowd has “always known” who’s who. “I’ve been out there all over the country with President Trump,” he said.