(CNN) After Georgia Republican Sen. Johnny Isakson announced Wednesday he was resigning his seat at the end of the year, it took less than an hour for the state's Republican machinery to spin into action.

It's up to Brian Kemp, Georgia's Republican governor, to appoint Isakson's replacement, and for a state that's been in GOP hands for nearly two decades, there's no shortage of candidates vying for the role.

News of Isakson's retirement was quick to circulate among politicos at a Chamber of Commerce event at the Atlanta Braves' SunTrust Park on Wednesday morning. One veteran Republican operative, Eric Tanenblatt, stepped out to take a call from a reporter. He wasn't alone. As he sat in the empty stadium seats, Tanenblatt noticed several other connected Republicans had also stepped out and were on their phones, either speaking quickly into the receivers or furiously texting.

Georgia Republicans spent much of Wednesday doing two things: emphasizing how important it was to honor and commemorate Isakson's long career before considering who might come next -- and then trading gossip, rumors and news about who might fill the role.

By the end of the day, more than a dozen names were being floated as possible appointees. The shadow primary to be Georgia's next Republican senator was underway.

Shortlist

Within minutes of Isakson's announcement, a consensus shortlist formed. On it, according to multiple GOP operatives familiar with Georgia, are state attorney general Chris Carr, Rep. Doug Collins, the ranking member of the House Judiciary Committee, and Georgia's current lieutenant governor, Geoff Duncan. Carr was chief of staff for Isakson for six years. His wife Joan currently has the same job. Duncan on the other hand is seen by many to have a close relationship with Kemp.

"There's probably a dozen more you could add to that list," said Tanenblatt, who by the end of the day was also being floated as a potential choice, according to one Republican operative. When asked by CNN if he would accept the job, Tanenblatt, a former chief of staff to then Gov. Sonny Perdue, denied he was "vying for anything."

Another popular name, Nick Ayers, the former chief of staff to Vice President Mike Pence, quickly popped his own trial balloon. Even before he left the White House this year to return to his home state, there were whispers that Ayers was interested in running for governor. But in a statement Wednesday afternoon (preempted by a lengthy paragraph of praise for Isakson), Ayers shut the door on accepting an appointment to the Senate.

"Governor Kemp has a number of great options to choose from who will represent our state with success and distinction — but I won't be one of them," Ayers said.

A special election

Reelected in 2016, Isakson will have only filled out half of his six-year term when he resigns on December. State law requires a special election to be held the following November to finish the term. Kemp's appointee will likely have a built-in advantage in the 2020 special election, but it will hardly be the only competitive election in the Peach State next year.

There's incumbent Republican senator David Perdue's reelection bid. Two congressional districts in the metro Atlanta suburbs, one held by each party, are already top targets for the other party. Every seat in the state general assembly, currently controlled by the GOP, is up for reelection.

And then there's the presidential race, where Democrats are hoping Donald Trump's relative unpopularity with swing voters can prove Georgia is a purple, not red, state.

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"The Democrats have made it no secret they will compete in Georgia," said Charlie Harper, a Georgia-based Republican consultant and political writer. "This (the special election) gives them yet another prize to go after."

A defining choice for Kemp

The stakes are bigger than a mere seat in the US Senate. Instead, the choice to replace Isakson may be a test for the Republican Party in Georgia, a red state that has been teetering on the brink of turning purple. As in many states, the Georgia GOP finds itself split between two factions -- a conservative, pro-Trump wing and a business-aligned "Chamber of Commerce" wing.

While Kemp ran in 2018 as a pro-Trump, gun-toting, tough-on-immigrants conservative, his victory was the narrowest for a Republican governor since Sonny Perdue's win in 2002. Democrat Stacey Abrams came within 55,000 votes (less than two percentage points) of upsetting him.

Perhaps in recognition of the changing politics, Kemp's been more temperate in his governance. Among his appointments, for instance, are the state's first Hispanic insurance commissioner and two black women judges on the courts in two Atlanta suburban counties, Cobb and Gwinnett.

Kemp may need to make a similar calculation with his selection to replace Isakson, who gained a reputation as a relative moderate within the GOP. As one Georgia Republican put it to CNN, an ideal appointee might be one that can appeal to suburban women who have been turned off by Trump's influence on the Republican Party.

The right choice from Kemp to replace Isakson could put Republicans in a good position to prevent a Democratic foothold in Georgia. The wrong choice could not only make the special election competitive but galvanize Democrats to push their position in Atlanta's growing and diversifying suburbs, where the GOP lost considerable ground in the 2018 midterms.

There are implications for Kemp himself. Whichever party controls the state's general assembly after next fall's elections will determine new congressional apportionment following the 2020 census. More favorable districts for Democrats in 2022 means more potential footholds -- in a year when Kemp will be up for reelection.

"My desire would be to use this as an opportunity to broaden our base," Tanenblatt said. The problem, according to another Georgia GOP operative, is that much of the GOP's bench, after years of total control, remains populated by "old white guys."

But selecting a replacement for Isakson who lacks appeal with the GOP's conservative faithful could be just as dangerous. The special election will be a "jungle primary," meaning any number of candidates from either party can qualify for the ballot. The risk is that the incumbent Republican that Kemp appoints could have to fend off challengers from both the Democratic Party and his own.

"This is where you're really going to get to see Brian Kemp's vision for the state," Harper said.