How will U.S. Sen. Johnny Isakson's replacement be chosen?

ATLANTA — After 40 years of services as a lawmaker, Sen. Johnny Isakson announced Wednesday morning that he is resigning his U.S. Senate seat because of health reasons.

He will leave at the end of December. Once he vacates his seat, Gov. Brian Kemp will announce someone to fill Isakson's vacancy until a special election is held.

[PHOTOS: Sen. Johnny Isakson through the years]

Then candidates from all political parties will compete against each other in November 2020, creating the possibility of many candidates in one race and the likelihood of a runoff Jan. 5, 2021.

A runoff is required if none of the candidates receives a majority of the vote. There will be no primary election for the Senate seat.

[READ: Georgia Senator Johnny Isakson hospitalized after falling at D.C. apartment]

"The governor will likely look the congressional delegation of Georgia to keep some seniority intact," Crane said. "You're looking at some names like Congressman Tom Graves of the 14th, Congressman Doug Collins of the 10th, former Congressman Jack Kingston, who was in the delegation before he ran against David Perdue. And then names like Chris Carr, our attorney general, and the lieutenant governor of Georgia, Jeff Duncan, is very close with the governor."

The winner of the special election will serve the remainder of Isakson's six-year term, which ends in 2022, and then another election will be held for a full term.


"Georgia will be the only state in the country with two U.S. senators up in the same election," Crane said.

Crane said to expect to see a lot of money being pumped into Georgia as the state's relevance in the 2020 race just shot up with Isakson's resignation announcement.

"The Republican National Senatorial Committee can't finance two senatorial races in Georgia. So, they'll need a nominee who can raise a lot of his own money."

A similar special election played out in 2017, when 18 candidates ran to replace former U.S. Rep. Tom Price, whom President Donald Trump appointed as secretary of U.S. Department of Health and Human Services.

[READ: GOP Senator Johnny Isakson breaks with president on border policy]

That high-profile race went to a runoff, when Republican Karen Handel defeated Democrat Jon Ossoff.

Regardless of who gets named as Isakson's replacement, Crane said that person will have some big shoes to fill.

"He's one of the true class act gentlemen that reaches across the aisle and means it. He put 25 bills into law just in his Senate veterans committee chairmanship."

Republican U.S. Sen. David Perdue will also be on the ballot in 2020, along with the winner of the Democratic Party primary. Three Democrats are already in the race: former nominee for lieutenant governor Sarah Riggs Amico, Clarkston Mayor Ted Terry and former Columbus Mayor Teresa Tomlinson.

Mark Niesse with The Atlanta Journal-Constitution contributed to this article.