Accepting this preliminary victory before it was clear who he would face in the runoff, Perdue told supporters Tuesday night: "One thing we did do tonight, we retired three career politicians—and we've got one more to go." If he prevails, he will face Michelle Nunn, a former nonprofit executive who's considered national Democrats' strongest new candidate this year, in November. As a testament to the swiftness of his rise, Perdue does not yet have a Wikipedia page.

Perdue's sudden popularity confounds the running tally in Washington, where scorekeepers are trying to mark down every GOP primary as a win for either the Tea Party or the Republican establishment. Perdue's pedigreed profile, as well as some conciliatory rhetoric on budget issues, would seem to put him in the latter category. But he has styled himself an antagonist of all things Washington and labeled his opponents "career politicians." In a debate over the weekend, Perdue pledged not to support Senate Minority Leader Mitch McConnell to lead the Republican caucus. At an election-eve rally at a private-jet hangar outside Atlanta on Monday, Perdue was joined by Herman Cain, the scandal-tarred former presidential candidate, who still hosts a popular conservative talk-radio program in Atlanta.

"The reason I support David Perdue is real simple," Cain told the crowd. "He is not going to become a part of the status-quo establishment. What we need most are people who are not afraid to rock the boat, to solve problems and put bold ideas on the table." In a typically nonsensical Cainian flourish, he concluded: "Someone asked me last week, 'Why are you supporting David Perdue?' My answer was real simple: There's no better choice!"

The principal reason for Perdue's rise was a clever campaign ad. Made by Fred Davis, the man behind John McCain's ad deeming Barack Obama a "celebrity" akin to Paris Hilton in 2008, the Perdue spot opened with a scene of four crying babies, names printed on their white onesies. "Jack" held a pair of glasses, "Paul" and "Phil" toyed with stethoscopes (Broun and Gingrey are physicians), and "Karen" wore pearls. "Help me change the childish behavior up there," Perdue said, as a picture of the Capitol lawn crawling with crying babies flashed onscreen.

The gimmick was a sensation, and Perdue has repeated the motif in ads since then. The babies also are pictured on the RV in which he's been touring the state. When I asked Perdue if the ad had been a game-changer, he said it had, and repeated a line from its script: "I'm running against four politicians with 63 years in office between them," he said. "If they were going to make a difference, they would have done so by now. The babies are memorable, they're subliminal, but the message is also strong."

Perdue told me that if elected, he would be an economics-focused senator who would draw on his business expertise while pushing for term limits. He criticized Republicans for failing to solve America's biggest domestic problems when they were in power from 2000 to 2008. "We really didn't solve the two or three critical issues around health care, so we inherited the Affordable Care Act," he said. "We haven't had an energy policy in forever .... Those were serious problems, and I didn't see any solutions coming from the Republican Congress."