Donald Trump picks Mike Collins over Derek Dooley in race to determine who will face Democrat Jon Ossoff in November midterms.

United States President Donald Trump has made a late endorsement in a Republican run-off for a key US Senate race in Georgia ahead of the US midterm elections.

In a post on his Truth Social account, Trump threw his support behind US Representative Mike Collins over former football coach and political newcomer Derek Dooley.

Collins and Dooley will face off in a Republican run-off race on Tuesday to determine who will challenge incumbent Senator Jon Ossoff, a Democrat, in the midterm election in November.

In a post on Truth Social, Trump praised Collins for being a staunch supporter of his Make America Great Again (MAGA) movement and a “true friend, fighter, and WARRIOR”.

Ossoff entered office in 2021 as part of a blue wave in Georgia that saw the majority of the state vote for former US President Joe Biden, as well as his fellow Democrat, Senator Raphael Warnock.

Georgia, which had for decades been dominated by Republicans, swung back towards Trump in the 2024 vote. Defeating Ossoff is seen as one of the Republicans’ best chances at claiming a new seat in the 100-member chamber, where they are hoping to hold on to their slim 53-seat majority.

Democrats are hoping to win control of both the House and the Senate in November, which would create a major bulwark against Trump’s agenda during his final two years in office.

Republican divides

Trump’s endorsement pits Collins against Georgia’s Republican Governor Brian Kemp, who has supported Dooley.

Kemp has remained generally supportive of Trump, but has faced off with him on several issues, notably Trump’s evidence-less claims that the 2020 election in Georgia was marred by fraud.

Dooley has said he did not vote in 2016 or 2020 when Trump was on the ballot, and has maintained that the election results in Georgia were legitimate.

Collins carried about 40 percent of the vote during Georgia’s Republican primary on May 19, with Dooley taking about 30 percent. Representative Buddy Carter, who did not advance to the run-off, came in a close third.

It remains unclear how big of an impact Trump’s endorsement will have. He made the announcement after early voting had already ended for the run-off.

Trump’s endorsements have seen mixed results in the primary season.

Trump’s decision to back Texas Attorney General Ken Paxton was seen as aiding in the MAGA loyalist’s defeat of US Senator John Cornyn in Texas’s primary run-off.

Cornyn had widely been viewed as the strongest Republican candidate to take on Democratic challenger James Talarico in the general election.

In Iowa, Trump’s late endorsement of US Representative Randy Feenstra did not give him the bump needed to defeat fellow Republican Zach Lahn in the gubernatorial primary race.

Beyond the run-off in Georgia, Alabama will also hold several primary run-offs on Tuesday. That includes a Republican race for the solidly red seat of US Senator Tommy Tuberville, who is running for governor.

Oklahoma and the federal district of Washington, DC, will also hold primary votes.