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(CNN) —  

Democrat Kyrsten Sinema raised concerns 11 years ago about imposing tougher penalties against individuals who solicit underage prostitutes because they may appear older than their ages, according to video of her remarks reviewed by CNN.

Those comments are coming to light in a new GOP attack ad as Sinema – who is now a US House member – is running in a high-profile race against Republican Rep. Martha McSally to fill the Senate seat vacated by retiring GOP Sen. Jeff Flake. Sinema stands a serious chance of picking up the seat, giving the Democrats a shot at retaking the Senate majority.

In a February 2007 state House hearing when she was an Arizona legislator, Sinema raised concerns about a bill that toughened penalties against individuals soliciting prostitutes, saying, “I don’t think that’s fair.”

As a former social worker at an elementary school, she said there were “children at my school who were 12, 13 years old and some of these children looked older than me.”

Sinema added that she had “real concern” for individuals who solicited child prostitution and could face a class 2 felony for “unknowingly soliciting sex from a 12-year-old who appeared to be a 20-year-old.”

According to video of her remarks reviewed by CNN, Sinema did speak out against child trafficking in that hearing, and she eventually voted for an amended version of the bill after raising concerns about the measure.

Sinema’s campaign called the ad deeply misleading and said it obscured her record combating child trafficking. Campaign aides argued that Sinema has a history of seeking to stop child trafficking, pointing to several bills she worked to pass to address the matter while serving in the state Legislature.

“Kyrsten voted for this legislation to toughen penalties for child trafficking and in the same remarks this latest false attack ad misleadingly edited, she spoke out forcefully against sex trafficking,” said campaign spokeswoman Helen Hare. “Kyrsten’s first job was as a rape crisis counselor and she has dedicated her career to defending women and children from abuse and assault.”

Hare called the ad a “false attack on Kyrsten’s clear record of standing up for women and children.”

The ad, bankrolled by the GOP super PAC Defend Arizona, spotlights Sinema’s 2007 comments and says: “That’s just wrong.” The ad fails to note her position in favor of the legislation to strengthen penalties on individuals who engage in child prostitution, instead saying her position “allowed men caught with child prostitutes to beat the rap.”

Defend Arizona plans to air the ad statewide, according to a spokesman for the group. The group of largely Arizona business leaders also spent nearly $1 million to oppose Republican primary challenger Kelli Ward’s candidacy.

The 2007 bill at issue would have made child prostitution a class 2 felony and eliminated the defense that an individual could not have known the age of the prostitute when soliciting sex from a prostitute as young as 15 years old. After Sinema and some others raised concerns at the hearing, the bill was amended to give a defense for people who solicited prostitutes as young as 15 “if they could not reasonably have known the age of the minor.”

The bill was opposed only by one member on the panel, Republican Andy Biggs, who is now a US congressman. A Biggs spokesman could not be reached for comment on the matter.

According to video of her remarks at the 2007 committee hearing, Sinema said that “we can all agree that sex trafficking, period, is wrong, and that child prostitution is worse than regular prostitution. We all agree prostitution is bad.”

“If you’re going to go out there and solicit sex or pimp for a living, like putting other young people on the street who’ll be solicited for sex, that one of the risks that you have to take when you’re engaging in already illegal activity is the knowledge that, if the person perhaps told you that they were a different age than they were, that you can be penalized more heavily if that person lied about their age,” Sinema said in 2007, according to video of her remarks.

“I don’t think that’s fair,” she added at the time. “I don’t think there’s any disagreement that pimping is wrong and prostitution is wrong and that johns shouldn’t be going out and getting prostitutes anyway.”

Sinema added: “I’m just not convinced that enforcing a strict liability on those johns who are engaging in prostitution is really the answer, and as a former social worker at an elementary school, there were children at my school who were 12, 13 years old and some of these children looked older than me. They were much more – I mean, definitely sophisticated, developed – and if I had seen a number of my former students in a place other than in a sixth-grade classroom, I would not have known that those children were 12 instead of 19 or 20. And so I do have a real concern for those individuals, and if one of those young girls were conscripted into prostitution and a john were to approach her, he’d be facing a class 2 felony for unknowingly soliciting sex from a 12-year-old who appeared to be a 20-year-old.”

The attack ad is the latest in a brutal contest between Sinema and McSally to become the first female US senator to represent Arizona.

McSally began airing her first ad attacking Sinema even before she secured the Aug. 28 Republican primary. The ad shows side-by-side pictures of McSally, an Air Force veteran, in her flight suit and Sinema in a pink tutu at an Iraq War protest. Sinema’s campaign dismissed the ad as a desperate and misleading effort to avoid a discussion about McSally’s “deeply unpopular” agenda.

Update: This story has been updated with additional context about what happened to the 2007 bill after the committee hearing.

CNN’s Veronica Stracqualursi contributed to this report.