Sen. Johnny Isakson announced Wednesday that he will resign his Senate seat at the end of the year, setting up a potentially competitive race in 2020 in a key electoral state. 

The Georgia Republican, who chairs both the Veterans’ Affairs and Ethics committees, has Parkinson’s disease and has been recovering from a fall that took place in July. A statement from Isakson’s office also said the senator had a surgical procedure earlier this week in Marietta, Georgia, to remove a carcinoma from one of his kidneys.

Isakson’s current term was not set to expire until 2023. 

“In my 40 years in elected office, I have always put my constituents and my state of Georgia first. With the mounting health challenges I am facing, I have concluded that I will not be able to do the job over the long term in the manner the citizens of Georgia deserve,” Isakson said in a statement. “It goes against every fiber of my being to leave in the middle of my Senate term, but I know it’s the right thing to do on behalf of my state.” 

Under Georgia law, Gov. Brian Kemp, a Republican, will be able to make an appointment to fill the unexpired term until the next regularly scheduled statewide elections, meaning there will likely be two Senate seats on the ballot simultaneously in 2020. Georgia’s junior senator, Republican David Perdue is seeking reelection. 

Whoever wins the special election for Isakson’s seat would serve for the remaining two years of the term and could run for a full term in 2022, when Kemp also faces reelection.

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Isakson said he notified Kemp of his pending resignation effective Dec. 31. He also said he plans to be back on Capitol Hill when the Senate returns one week after Labor Day.

“I look forward to returning to Washington on September 9 when the Senate goes back into session. And after December 31, I look forward to continuing to help the people of Georgia in any way I can and also helping those who are working toward a cure for Parkinson’s,” he said.

Several Democrats are already running to challenge Perdue next year, including former Columbus Mayor Teresa Tomlinson, 2018 Georgia lieutenant governor nominee Sarah Riggs Amico and Clarkston Mayor Ted Terry. All three are remaining in the race against Perdue, the Atlanta Journal Constitution reported Wednesday afternoon.

Jon Ossoff, the Democratic nominee in the 2017 special election for the Atlanta-area 6th District, hasn’t yet made a decision about running against Perdue, but he now has another race to consider. 

One prominent Georgia Democrat has already ruled out a run for Isakson’s seat. Stacey Abrams, who narrowly lost a race for governor last year, had already rebuffed recruiting efforts by national Democrats to challenge Perdue.

An Abrams spokesman said the former state House minority leader “will lead voter protection efforts in key states across the country, and make sure Democrats are successful in Georgia in 2020.”

“While she will not be a candidate herself, she is committed to helping Democrats win both Senate races next year,” the spokesman said. 

As for the GOP appointment to replace Isakson, Republicans with knowledge of the state are keeping an eye on state Attorney General Chris Carr, who used to be the senator’s chief of staff, as well as GOP Reps. Doug Collins and Tom Graves and former Rep. Karen Handel, who is currently running to reclaim the 6th District seat she lost last fall. Other names being mentioned include Lt. Gov. Geoff Duncan and former Gov. Sonny Perdue, who is now Agriculture secretary in the Trump administration. 

Inside Elections with Nathan L. Gonzales now rates both Georgia Senate races Leans Republican.

Simone Pathé contributed to this report.