Georgia GOP Sen. Johnny Isakson said Wednesday he would retire at the end of the year as he continues battling Parkinson’s disease, setting up two elections for key Senate seats in the Peach State in 2020.

Isakson has served in the Senate since 2005, won his third term in 2016 and wasn’t up for re-election until 2022.

“In my 40 years in elected office, I have always put my constituents and my state of Georgia first,” Isakson said in a statement, the Atlanta Journal-Constitution reported.

“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. 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.”

Isakson, 74, has taken several bad spills since revealing that he has Parkinson’s, which hampers balance and mobility.

Three Democrats had already announced a challenge to Sen. David Perdue, Georgia’s other senator, a first-term Republican up for election in 2020.

Isakson’s withdrawal was expected to attract other Democrats, who see Georgia as competitive and remain mindful of Democratic Sen. Doug Jones’ win in neighboring Alabama, despite President Trump’s support for his GOP opponent, Roy Moore, who had been accused of sexual misbehavior with young women.

It was unclear whom GOP Gov. Brian Kemp would appoint to Isakson’s seat, though candidates include Attorney General Chris Carr, Georgia Senate President Pro Tem Butch Miller and Rep. Doug Collins, the paper reported.

Isakson was just the latest incumbent Republican lawmaker to not seek re-election.

Others include Reps. Rob Woodall of Georgia, Susan Brooks of Indiana, Paul Mitchell of Michigan, Pete Olson of Texas and Martha Roby of Alabama

Also, Reps. Rob Bishop of Utah; Mike Conaway, Will Hurd and Kenny Marchant of Texas; and Sean Duffy of Wisconsin.

Democratic retirements include Reps. Jose Serrano of New York and Dave Loebsack of Iowa.

Democrats control the House while Republicans hold the Senate, and each party is striving to maintain its majority while trying to flip the chamber they do not control.