Georgia Republicans are dumbstruck.

How did a candidate who amounted to an also-ran in the 2004 open seat Senate race transform himself into a top-tier presidential candidate in just 7 years?

Answers are few and far between. But, a look back at the only political race Cain had run prior to his 2012 presidential candidacy still provides some insight.

The seat came open when Sen. Zell Miller announced his retirement in January 2003. Republican Rep. Johnny Isakson was the establishment favorite from the start but his main primary opponent was expected to be then Rep. Mac Collins.

But Cain proved the better candidate, eventually taking 26 percent of the vote to 21 percent for Collins. Of course, neither Cain nor Collins came anywhere close to Isakson, who won 53 percent and, in so doing, avoided a potentially problematic runnoff.

Isakson confidantes say avoiding the runoff was preferable, but that they weren’t terribly worried about beating Cain head-to-head if it came to that.

“I would think that he probably hit his high watermark there” at the end, said longtime Isakson supporter Rogers Wade, who is chairman of the board at the conservative Georgia Public Policy Foundation. “He was a phenomenon as a black businessman running a statewide race. He was a curiosity.”

Ericka Pertierra, a top aide to Rep. Tom Graves (R-Ga.) who worked on the 2004 Cain campaign, said Isakson’s campaign was wary of her candidate, though. She noted that Isakson’s side dropped mail pieces at the end pointing out that Cain had contributed money to Democratic Sen. Bob Kerrey (D-Neb.) and tried to paint him as a sympathizer of Democratic lightning rods Hillary Clinton and Ted Kennedy.

“Isakson didn’t want to go to a runoff — no way,” Pertierra said. “They dropped mail saying Cain was a Democrat.”

The campaign wasn’t a total failure for Cain. Despite his newcomer status, he finished ahead of a sitting member of Congress. Observers say Cain’s showing created a sense that he would be a formidable candidate for a lower-tier statewide office like Agriculture Commissioner, but that never materialized, and Cain was diagnosed with cancer in 2006 and landed his Atlanta radio show in 2008.

At the same time, political watchers in Georgia did see flashes of the rhetorical flair that has characterized Cain’s rise in the Republican presidential race this year.

“He did leave a favorable impression with a lot of Republican voters,” said Charles Bullock, a longtime Georgia political analyst at the University of Georgia. “It was clear that he was making a move and was going to be more than a throw-away candidate with 3, 4, 5 percent.”

Bullock and others say Cain’s 2004 campaign was run much like his current one – with little staff and on a meager budget.

The difference between that campaign and this one, it seems, is that Cain has national platform afforded him by the crowded debate schedle to get his message out, whereas his team struggled to get Isakson to debate at all in 2004.

With all that said, even Cain’s longtime supporters didn’t quite see his rocket-like ascent in the presidential race coming.

“Maybe I’m a little bit surprised,” Pertierra said of Cain’s top-tier status. “I did not think that he was able, with a lack of money, to be able to get his message out, and that’s just being honest. But he’s done an effective job of getting his message out.”

(For more on Cain’s 2004 campaign, making sure to check out Molly Ball’s great piece over at The Atlantic.)