Former Senator David Perdue plans to announce a primary challenge against Georgia's incumbent Republican Gov. Brian Kemp on Monday, according to a source familiar with Perdue's thinking.

Why it matters: Perdue's challenge to his former ally Kemp sets up an unprecedented "scorched earth" battle between Georgia Republicans fueled by former President Donald Trump, in the battleground state. The news was first reported by Politico.

• The news comes days after former Democratic candidate Stacey Abrams announced her second bid for the seat.
• Two people familiar with the discussions told Axios’ Jonathan Swan that Trump signaled to Perdue weeks ago that if he ran, he could expect an endorsement from the former president.

Catch up quick: Since Kemp resisted Trump's pressure to overturn the state's 2020 election results, Trump has pledged to campaign against the incumbent governor he endorsed in 2018 and has been encouraging Perdue to challenge Kemp.

• Biden won Georgia in 2020 by a little over 12,000 votes. Republicans also lost both Senate seats to Democrats: Perdue was defeated by Jon Ossoff, and Raphael Warnock beat Kelly Loeffler.
• Trump openly asked Perdue if he planned to run against Kemp at a September rally in Perry, Georgia.

The irony is that Trump has said that it was David Perdue and his cousin, former agriculture secretary and former Georgia Gov. Sonny Perdue, who convinced him to endorse Kemp in his 2018 Republican primary.

What they're saying: “Perdue’s only reason for running is to soothe his own bruised ego, because his campaign for U.S. Senate failed to inspire voters at the ballot box — twice," said Cody Hall, Kemp's director of communications and senior adviser.

"Governor Kemp has a proven track record of fighting the radical left to put hard-working Georgians first, while Perdue is best known for ducking debates, padding his stock portfolio during a pandemic and losing winnable races."

Former Speaker of the House Newt Gingrich called Perdue "the one figure who could unify Georgia and the one person who could beat Stacey Abrams."

What’s next: “Kemp and Perdue have overlapping bases and donors in many ways, so personal relationships are more important than ever,” said Republican Georgia strategist Brian Robinson. Who was nice or responsive to whom “all of a sudden matters a great deal.”