Representative Mike Collins, a Trump-endorsed immigration hard-liner who has drawn headlines with provocative social-media posts, faces Derek Dooley in the Republican Senate primary runoff in Georgia on Tuesday.

Here are five things to know about Mr. Collins, 58, a second-term representative from rural central Georgia who led Mr. Dooley by about 10 percentage points in the first round of voting, in May.

1. He received a late endorsement from President Trump. Mr. Collins has some unique ties to the president, who endorsed the representative on Sunday in a Truth Social post that described Mr. Collins as “Friend, Fighter, and WARRIOR.” The first bill Mr. Trump signed after returning to office was a bill sponsored by Mr. Collins. The measure, the Laken Riley Act, targeted unauthorized immigrants charged with nonviolent crimes for deportation. Mr. Collins’s campaign website describes him as a “constant” presence at Trump rallies.

2. His hard-line immigration views are at the heart of his campaign. Mr. Collins has pointed to the Laken Riley Act and his broader positions on immigration during his run for Senate. That bill is named for a 22-year-old Georgia nursing student who was killed in 2024 by a migrant from Venezuela who crossed into the United States illegally. Her family has endorsed Mr. Collins, as has the union representing border agents. After Bishop Mariann Edgar Budde of the Episcopal Diocese of Washington directly urged Mr. Trump in 2025 to display mercy on behalf of immigrants, Mr. Collins wrote on social media that she “should be added to the deportation list.”

3. He built a trucking company. Mr. Collins and his wife, Leigh Ann, started a trucking company in the 1990s. The company, Collins Trucking, based about 40 miles southeast of Atlanta in Jackson, Ga., hauls freight across the Midwest and Southeast. It has more than 100 employees, according to his campaign. Mr. Collins has leaned into his trucking past as he runs for the Senate. In a video announcing his campaign, he said, “It’s time to send a trucker to the U.S. Senate” to put Georgians “back in the driver’s seat.”

4. He has a history of incendiary social media posts. Mr. Collins, who posts frequently, once responded to videos of white male University of Mississippi students taunting and jeering a Black female student at a pro-Palestinian protest by writing, “Ole Miss taking care of business.” (He later issued a lengthy statement saying that if anyone had treated someone “improperly because of their race, they should be punished appropriately.”) And after the assassination attempt against Mr. Trump at a campaign event in Butler, Pa., in 2024, Mr. Collins wrote on social media that “Joe Biden sent the orders” and urged a local prosecutor to bring charges against the Democratic president. After the post, the conservative editorial board of The Wall Street Journal compared Mr. Collins’s behavior to that of “the village idiot.”

5. He faces an ethics probe: The House Ethics Committee is looking into allegations that Mr. Collins’s office paid a district office intern who had a romantic relationship with the representative’s chief of staff but did not actually work in the office. Mr. Collins said in an April primary debate that the inquiry was based on a “bogus claim” filed anonymously. “Anybody can file a complaint,” he said.