The month of May was good to David Perdue. He was the cool but non-threatening rebel, a Fonzie who predicted happy days if only Republicans would elect an outsider to the U.S. Senate.

He was the top vote-getter in a seven-candidate field.

But a funny thing has happened on the nine-week road to a July runoff. GOP rival Jack Kingston and his allies have given Perdue – he of the turned-up, denim-jacketed collar – an involuntary makeover.

They have turned The Outsider into The Renegade. Hundreds of thousands of dollars are being spent to portray the former Dollar General CEO as the dangerous stranger – think Marlon Brando conquering a small town on his thundering hog.

Kingston has piled up endorsement after endorsement from GOP regulars, each of whom warns that the Fortune 500 executive and first-time candidate could be a chaos-loaded Trojan horse. Their evidence: Perdue has never stuffed a campaign envelope or pounded a campaign sign into the ground, and has been a scofflaw when it comes to paying his GOP dues.

Reliable polling is scarce, but it’s safe to say that the last month has seen Perdue shift from frontrunner to underdog. Perdue himself admits as much.

Take the issue of endorsements. “We knew we would not get the establishment to get excited about us,” Perdue said in an interview this week.

He’s got radio talk show host Herman Cain on his side, and some state lawmakers. But the candidate said he doesn’t expect an army of veteran surrogates to flock to his cause in the next three weeks.

“I welcome every one of them, but I’m not anticipating any new endorsements,” Perdue said.

Despite his personal wealth, Perdue acknowledged that he is now at a financial disadvantage, given the money being spent by groups like the U.S. Chamber of Commerce in support of Kingston. Perdue said he would “probably” contribute more personal funds to his campaign – June 30 is the next campaign finance reporting deadline, and a large number is important.

“I don’t know how much, but I’m going to make sure we are funded to get the message out. Right now, our fundraising is doing very well,” he said.

Perdue was in his Buckhead campaign office, which is located above state headquarters of the GOP establishment that now shuns him. Newt Gingrich used the same space during his 2012 presidential run.

As Kingston has worked to redefine Perdue, Perdue is now attempting to identify Kingston, a 21-year veteran of Congress, as the “incumbent” in the race – and a willing participant in a George W. Bush-era decline of Republican fortunes. Last week’s Gallup poll, showing Congress with a historically low approval rating of only 7 percent, didn’t hurt.

“I’ve been reminding people that — between 2000 and 2008, where was our landmark health care reform bill? Where was our tax reform bill? Where was our transportation bill? The only thing I saw then was we took the debt from $6 trillion in 2000 to $10 trillion in 2008,” Perdue said. “The Republicans lost the high ground then.”

Perdue’s new focus has been on Kingston’s role as a member of the House Appropriations Committee, and one of the largest contradictions within the Savannah congressman’s campaign.

“Jack’s being endorsed by the [U.S.] Chamber of Commerce, even though he supposedly disagrees with them on Common Core and amnesty [for illegal immigrants]. That should concern me as a voter, dramatically,” Perdue said.

This week, Perdue named Kingston the “king of earmarks.” In one three-year period, the Savannah congressman requested more – for a total of $211 million — than the rest of the Georgia delegation put together, Perdue charged.

But in making its case, the Perdue campaign also pointed out that Nathan Deal, now in the middle of a tough re-election bid for governor, made $10 million in earmark requests during the same period. A wise move to include the governor? “Probably not,” Perdue admitted.

The Outsider is also giving fresh emphasis to the need for term limits. The same Washington-based political action committees that keep members of Congress in office are the ones sabotaging any attempt to address a $17 trillion federal debt, Perdue argued.

And that, the candidate said, can be linked to criticism that he hasn’t paid his Republican dues. That he hasn’t licked enough envelopes.

“The current model is full of people that are doing that, and I admire that,” Perdue said. “But look at the results. The current model’s broken. I’ve spent 42 years licking envelopes and doing a lot of other things in the business world. I’m not going to apologize for that.

“Frankly, with only about 10 people in the U.S. Senate that have that background, I believe that’s one of the things that we need up there.

“The argument about non-participation in the process – it’s an empty comment, because [critics] don’t understand the bigger issue. The biggest issue is not moving through the machinations of a political structure within a party, so that you can be tapped one day to run for Congress. That’s what’s got us in this mess,” Perdue said.

Spoken like a true outsider. Or a renegade. One or the other.