Georgia U.S. Sen. Johnny Isakson returned to his beloved Senate this week for the first time since announcing his retirement armed with a secret plan.

The three-term Republican, who over two decades on Capitol Hill has honed a reputation as an affable dealmaker, is determined to pull off one last major bipartisan policy coup before his Dec. 31 departure date. On which thorny policy issue, he refused to say.

“I’m getting close to something I can tell you about, that I’ve been working on for some time,” Isakson said with a grin on Monday evening. “I’m not quite there yet.”

Isakson's renewed political resolve obscured the agonizing choice he made late last month to leave a job he loves in the face of mounting health problems.

The decision surprised his closest allies. Save for a small circle of longtime advisers, he even kept most of his staff in the dark until shortly before the news went public. It instantly upended Georgia politics by teeing up a second U.S. Senate race for November 2020, a contest that some believe could determine party control of the chamber.

Opening up about his decision in an interview with The Atlanta Journal-Constitution, Isakson, 74, said making the call to step down “was simple but it was hard.”

“My mother used to tell me listen to your body. And my body was telling me that I was getting to the point where I couldn’t fulfill 100% of my commitment to the job and do it right,” he said.

Fateful fall

Ever since he announced in 2015 that he suffered from Parkinson's disease, a progressive nervous system disorder, Isakson's team became adept at batting down stories about his future. He intended to finish up his term through 2022, they said, and some aides floated the possibility of him running for a fourth term as recently as May. That united front remained even as Isakson underwent two back surgeries in 2017 and started traversing the Capitol's marble corridors in a wheelchair.

The turning point came on July 16.

Isakson had recently moved into a more handicap-accessible apartment in downtown Washington after his longtime Capitol Hill condo, with a temperamental elevator and lots of staircases, became too difficult to navigate. On his second night in the new apartment, he tripped.

The fall was serious — he fractured four ribs and spent four days in the hospital and another six in inpatient rehab — but it was nearly much worse, and Isakson began thinking about whether he could continue his job in the U.S. Senate.

Then came two MRIs that cemented his decision. One scan revealed Isakson had torn his rotator cuff. A second found that a previous cancerous growth on his kidney known as a renal cell carcinoma had doubled in size.

“I was in a phase where I was asking myself ‘what in the world are you going to do?’” he said. “I had four broken ribs. I had a spot on my kidney. I was in the hospital. I’d had a bad fall, which was the fourth fall of significance I’d had in three years.”

Isakson shared his retirement decision only with a tight circle of confidantes: his wife Dianne and trio of longtime aides that included Chief of Staff Joan Kirchner Carr, her deputy Trey Kilpatrick and political adviser Heath Garrett.

The group then went to work to figure out timing. A dive into Georgia's Constitution found that Isakson would have to stay in office until late September 2020 to avoid a special election, something he said he wasn't physically able to do.

They waited until Isakson successfully had surgery on Aug. 26 to remove the malignant 2.3-centimeter growth on his kidney before finalizing plans for him to resign four months later.

He broke the news to the rest of his staff the morning of Aug. 28, shortly before the announcement was blasted out to the public. His office gave a heads-up to Gov. Brian Kemp but few others, and there was no pre-arranged deal to anoint an interim replacement.

“I didn’t want to be the talk of the town,” Isakson said about keeping his decision private until the end.

The announcement triggered a deluge of tributes from current and former colleagues in Georgia and Washington, as well as a rapid shadow campaign for his seat. The names of more than a dozen potential candidates quickly emerged, even as Kemp provided no clues about who he'd appoint to replace Isakson through next year.

For his part, Isakson said he would not advise Kemp about a potential successor unless asked. And he outlined an ambitious list of priorities for his months left in Washington, including securing new funding for the Savannah port, confirming a Georgia judicial nominee and wrapping up loose ends on the Senate Veterans’ Affairs Committee, which he leads.

Isakson said he was still adjusting to his new reality, one that includes a stricter diet, no more driving and a steady stream of goodbyes. In the meantime, he’s resolved to soak in his remaining time in the Senate.

He was in a chipper mood as he returned to Capitol Hill on Monday, greeting the elevator operator with a “hey darlin’,” and chuckling with colleagues for more than an hour on the Senate floor, his new walker within arms’ reach.

After the final vote of the evening, he huddled at the front of the chamber with Majority Leader Mitch McConnell, his longtime friend and ally. The conversation, he later let slip, was about the mysterious new legislative push on which he wouldn't elaborate.

“It’s my concoction that I think Democrats and Republicans will like a lot,” he said. “That’s why I’m cryptic about it… I made some good progress today.”