And by the time he announced his campaign for governor last summer, he had a November-friendly message that promised new jobs and modest tax cuts. The money soon followed: An astonishing $10.5 million – and he would have had more if not for a fundraising lull during the legislative session
It was the type of imposing juggernaut meant to scare others out of the race. Except it didn't. While a handful of high-profile contenders opted out, most Republicans who were already seriously considering the race wound up jumping in. Kemp, meanwhile, had already entered the contest months earlier.
The first major turning point in the campaign came in February when Delta Air Lines cut marketing ties with the National Rifle Association, prompting Cagle to orchestrate the defeat of a lucrative proposed tax break for the Atlanta-based airline.
While the move infuriated Democrats and business leaders, it was hailed by conservatives and earned him the NRA's coveted endorsement. At the time, some GOP operatives saw it as a master stroke that could help him win the May 22 primary without a runoff.
But as the five-man contest neared, that prospect dimmed. With poll numbers parked around 40 percent, he made the calculated decision to attack Hunter Hill, a former state senator in the thick of the race, to help Kemp get in the runoff.
At the time, Cagle’s advisers believed Kemp would be a more beatable adversary. He didn’t have Hill’s appealing military background, he didn’t have the same fundraising chops and he didn’t have the “outsider” advantage since both had offices across the hall from each other under the Gold Dome.
More importantly, to Cagle's advisers, Kemp had a series of miscues as the state's top elections official that he was going to exploit. Pretty soon, Cagle unleashed one attack after another labeling his rival "inKempetent" and questioning how he could manage the state's top office.
The primary vote revealed new weaknesses. Despite his huge fundraising advantage, Cagle captured just 39 percent of the vote, and pollsters found a soft spot of enthusiasm for the candidate. He also failed to win a majority of his native Hall County, which was the difference-maker in the 2010 GOP race.
Then came the biggest bombshell of the race: The secretly recorded tape. It was made by Clay Tippins, a former GOP rival who used an iPhone in his coat pocket to tape a 90-minute conversation with Cagle, purportedly about offering an endorsement.
Tippins said he was so disgusted with Cagle's candid remarks that he wanted to go public, and the nine-minute segment of the tape he cut with his daughter's help rocked the race. In the muffled audio, Cagle admits to supporting "bad public policy" to undercut Hill's bid for office.
Cagle's campaign first hoped the tape would blow over, but another snippet was released with Cagle lamenting that the primary was a race "over who could be the craziest." For Kemp, it was an epic gift: He had long tried to paint Cagle as a phony conservative; now he could use his own words against him.
The secretary of state ratcheted up the pressure in other ways, tacking to Cagle’s right on every major policy issue. He pledged the nation’s toughest abortion restrictions, painted himself as the more loyal Trump supporter, portrayed Cagle as squishy on gun rights.
As his poll numbers flagged, Cagle seized on Atlanta Journal-Constitution stories about Kemp's troubled investments in a Kentucky seed-crushing plant and questionable campaign contributions to accuse him of depriving farmers of their livelihood and tacitly condoning sexual assault.
And in the final stretch, he lashed out. He pushed a false line that the "fake news media" was colluding with Kemp – which caused plenty of snickering – and said, definitively, that the secretary of state would lose to Democrat Stacey Abrams in November.
He also hit the campaign trail with an underdog’s flair that reminded his supporters of his 2006 upset defeat of Ralph Reed, who was the Casey Cagle of that race – a presumptive front-runner with an unstoppable-seeming campaign.
Cagle’s strong performance in the final televised debate last week energized his staffers, and the next day he nabbed Gov. Nathan Deal’s endorsement.
That was seen as a turning point for his campaign – the governor is one of the most popular Republicans in the state – even though his announcement was rather understated: His support came during a question-and-answer session after an unrelated event.
And then came the final jolt to the race: Trump’s tweet giving Kemp his “full and total” endorsement. It popped on a Wednesday afternoon, and there’s still question about who was behind it. But it might as well have been the nail in the campaign’s coffin.
“We had the momentum in this race,” said Kemp shortly after his victory, “but those endorsements by the president and the vice president poured gasoline on the fire.”
One insider showed a chart of Cagle's tracking numbers nose-diving after Trump weighed in. His supporters were deflated, his campaign trail appearances more muted. Vice President Mike Pence's visit Saturday only reinforced the point. By then, Kemp started acting like a front-runner, looking past Cagle toward the November election.
For some undecided Republican voters, Trump’s endorsement suddenly gave them a new way to support the president. Chuck Damren, a Lawrenceville Republican, was already leaning toward Kemp when the president weighed in. That helped seal the deal.
"It's important we fight together to keep our rights and our freedoms, and to go along with President Trump's agenda,” Damren said as he went to the polls.
In the final days, Cagle let loose. He amped up his negative attacks on Kemp – his final ad was particularly scathing – and hoped that low voter turnout favored his campaign.
But his attempts to counter with Deal’s support fell flat: While Trump sent a string of pro-Kemp tweets and Pence rallied supporters in Macon, the governor did little, if anything, publicly for Cagle after he formally endorsed him.
At one of his final campaign events on Monday, just before launching a fly-around tour, Cagle sounded a wistful tone about what could have been. He didn’t lament his attacks on Hill or the secret recording or the Trump endorsement. Instead, he vented about the negativity that dominated the nine-week runoff.
“It’s always easy to be a Monday morning quarterback and look back,” he said. “I wish we had run ads telling my story, the story of where I came from, to be able to be where I am today is a story of the American dream.”