Last spring, long before the candidates for governor started going after one another, before attack ads flooded the airwaves and before a couple of super PACs, a well-known blog and, finally, U.S. Sen. David Vitter’s trailing Republican opponents began talking about his “serious sin,” I asked Vitter whether he thought his 2007 prostitution scandal was fair game. This was his answer:

“Look, it’s a free country, and it may very well come up,” Vitter said. “I think if it comes up, and to the extent it comes up, it shows that my opponents are pretty desperate, quite frankly. Because I know, I know from traveling the state talking to all sorts of Louisianans, that they want to hear about solutions ... they’re not focused on somebody’s personal past.”

How naïve all that sounds today, as we rapidly approach a shockingly competitive runoff, as Vitter himself is looking increasingly desperate, and as his Democratic runoff opponent, state Rep. John Bel Edwards, is now seizing on the issue to go in for the kill.

Edwards, who emerged from the bloody four-way primary campaign largely unscathed, went there in a big way over the weekend. His new ad, timed to run during Saturday’s LSU-Alabama showdown, had already rocketed around the Internet by then. It offers a dramatic contrast between Edwards’ own military service and a congressional vote honoring fallen soldiers that Vitter skipped around the time he’s on record taking a call from a District of Columbia call-girl ring. “David Vitter chose prostitutes over patriots,” it concludes. “Now, the choice is yours.”

It’s the kind of ad that makes you sit up and take notice, but whether Edwards was wise to run it is a real question.

Despite his 40 percent primary showing to Vitter’s 23 percent, not to mention post-primary polls giving him a healthy lead, he’d be crazy to think the race isn’t going to be close. Louisiana is now a firmly Republican state, one that hasn’t elected a Democrat to statewide office in seven years, and no matter what else happens, the basic math is not his friend. So if the thinking is that Edwards needs to stay on offense, that makes sense.

Still, a big part of his appeal to date stems from the fact that he’s stayed above the fray. In part, he can thank the competitive Republican primary field for that. Vitter, Lt. Gov. Jay Dardenne and Public Service Commissioner Scott Angelle battled for a single runoff spot, but Edwards, as a Democrat, was everybody’s preferred opponent in the second round. So they left him largely alone, in a position to play the good guy, the one who went to West Point and can talk about “honor” and “integrity” without inviting snickers. There was never any doubt who was on the other end of that implicit contrast.

And the pro-Edwards forces had other options as well. An outside group could have sponsored the ad, allowing the candidate to keep his own hands clean.

On the other hand, by this point in the race, it’s hard to see Vitter playing a convincing victim. Despite his early prediction about how the race would go down, he long ago stopped holding up his end of the bargain he proposed last spring.

Vitter’s campaign has been stunningly short on those “solutions” that he insisted all those Louisianians wanted to discuss. Instead, it’s been one long televised diatribe, first against Angelle and Dardenne, and now versus Edwards. Since the runoff, Vitter has taken every opportunity to argue that an Edwards victory would be akin to electing President Barack Obama governor, despite their very different politics on issues ranging from gun rights to, most recently, the Keystone XL pipeline, and despite the fact that Dardenne crossed party lines to back the Democrat.

Vitter is also running an ugly, wildly distorted commercial suggesting Edwards’ stand on reducing incarceration rates for nonviolent offenders — one that he shares with many conservatives and that even Vitter seems to embrace — amounts to letting 5,500 “dangerous thugs” out of prison. And don’t forget that all this came on the heels of the discovery that Vitter had hired a private investigator to conduct surveillance on his adversaries.

Ironically, given the state’s leanings, Vitter started off with the upper hand on issues. It’s his own behavior, both past and present, that raised the question of character.

Edwards’ new attack ad may or may not mar his image as the race’s nice guy, but give him this. As Vitter suggested way back when, it’s a free country, and his past is fair game. And Edwards has now proven that he can hold up his end of a fight.

Stephanie Grace can be contacted at Read her blog at Follow her on Twitter @stephgracenola.