After Republican congressional candidate Martha McSally announced today that she supported changing federal gun laws to include those who are convicted of misdemeanor stalking on the list of prohibited possessors, Gabby Giffords' political action committee, Americans for Responsible Solutions, said it would be ending the run of a controversial TV ad one day early.

Pia Carusone, a senior adviser to Americans for Responsible Solutions, said she was pleased that McSally was moving away from her blanket opposition to expanding background checks.

"We're happy to see Martha McSally has changed her position on making it illegal for convicted stalkers to legally acquire firearms," Carusone said. "We hope her evolution on this issue continues."

But McSally spokesman Patrick Ptak said that McSally has always supported closing the so-called "stalker gap," although she had never addressed the issue before.

"Ron Barber's political allies never asked Martha's stance on the 'stalking gap' before running their disgraceful and false ad, and Martha's position has never changed on the issue," Ptak said.

The ad was the latest flashpoint in the tight race between McSally and Congressman Ron Barber (D-CD2).

McSally objected to the ad, entitled "Stalker Gap," after it launched last week because she herself had been the victim of stalking.

“Stalker Gap.", which was backed by a six-figure media buy on local and cable stations, is undeniably hard-hitting: It features Vicki Walker, a woman whose husband Daniel Walker and daughter Kara Walker were gunned down by Kara’s ex-boyfriend, Daniel Renwick, in 2000.

Renwick had made threats to kill Kara and her family just months earlier. There were plenty of signs of trouble: Renwick had beat Kara up and roared off while drunk with their child. After he was stopped by police, he eluded an officer who attempted to take him into custody and sped away, sometimes reaching speeds of 70 mph while the baby was in the back seat, according to a Tucson Citizen account.

In the ad, a tearful Vicki recalls that “My daughter was just 19 when she told her boyfriend their relationship was over, and he got a gun and he shot her and my husband. He had threatened her before. I knew—I just knew.”

A narrator then says: “Martha McSally opposes making it harder for stalkers to get a gun.”

After the ad aired, McSally cried foul, saying the ad was “personally offensive” because she herself was the victim of stalking.

"As someone who's experienced being stalked, I know what it feels like to worry constantly about when and where your stalker will appear next and what he'll do,” McSally said in a prepared statement. “I've had threats made against me and wasn't even safe in my own home or my car where my stalker broke in and held me in a hostage-like situation.”

McSally added that the ad was “degrading to all women and victims who have experienced this pain.”

Giffords’ husband, retired astronaut and U.S. Navy captain Mark Kelly, told the Weekly that he and Giffords stood by the ad.

“As a former elected official, Gabby understands that if you’re running to represent your community at any level, it’s essential that you make your positions clear on the big policy questions—and that includes the question of who in our country should have access to firearms,” Kelly said via email. “Undeniably, one category of people that should be denied access to guns is stalkers. This is about changing the law to protect lives.”

There is a gap in the law that allows people who are convicted of stalking to buy firearms. As it now stands, those convicted of felony stalking at the state level have their names added to the federal “prohibited possessor” list that is used for background checks when licensed firearm dealers sell guns.

But those convicted of misdemeanor stalking do not have their names added to the list.

Stalking laws vary from state to state (and federal law only addresses stalking if someone a state line while harassing a victim). In Arizona, stalking is a felony and anyone convicted of the crime is prohibited from buying a gun from a licensed dealer until their rights are restored, although they can still purchase a firearm from a second-hand dealer. But many other states treat stalking as a misdemeanor, which means those convicted of the crime do not have their names added to the list of prohibited possessors.

Sen. Amy Klobucher (D-Minn.) last year introduced the Protecting Domestic Violence and Stalking Victims Act of 2013, which would add the names of those convicted of misdemeanor stalking or of abusing someone they are dating to the list of those who are prohibited from possessing a firearm, but the legislation went nowhere.

McSally spokesman Patrick Ptak declined to discuss the details of McSally’s stalking episode, so it’s unclear whether police were involved or if her stalker was convicted of any crime.

McSally has previously said that she opposes changes in the law that would put more people on the list of prohibited possessors. In April, Team McSally deputy campaign manager Kristen Douglas told ABC News that McSally is “pro Second Amendment and believes our focus for preventing shootings should be on strengthening our mental health system and enforcing background check laws already on the books, not expanding those laws that will do little to prevent violence and infringe on the rights of law abiding citizens.”

When asked how much she supported the goals of the National Rifle Association on a scale from one to 10, McSally told a crowd of Republican supporters earlier this year that she saw herself as a 10.

But today, Ptak told the Weekly that McSally makes an exception to her previous opposition in the case of the stalker gap. McSally, said Ptak, does support expanding gun laws by “adding misdemeanor stalking to the list of criminal offenses that would keep dangerous individuals from obtaining guns in other states where stalking can also be a misdemeanor. Martha strongly believes we need to place a greater emphasis on the cause of gun violence by addressing our broken mental health care system and enhancing our ability to recognize and treat signs of mental illness.”

Ptak has not responded to a question as to whether McSally would support the Protecting Domestic Violence and Stalking Victims Act of 2013, which is opposed by the NRA.

“Stalker Gap” was condemned by the Arizona Republic editorial page, which called it “base and vile” for linking McSally to the killing of Daniel and Kara Walker. But other publications—including the Tucson Weekly and Slate—noted that the ad accurately portrayed the statements that McSally had made prior to today.

Kelly said that pointing out McSally’s statements on laws related to gun violence—and their consequences—is fair game.

“Our goal in founding this organization was to communicate directly, honestly and fairly with voters about where their candidates and elected officials stand on laws that reduce gun violence,” Kelly said. “We won't be deterred, but will never attack character and we will never veer from fact.”

Giffords, who survived being shot through the head in a Tucson mass shooting that claimed the life of six and wounded a dozen people besides the former congresswoman, formed Americans for Responsible Solutions with Kelly to push for gun-safety measures in the wake of the 2012 Sandy Hook Elementary School shooting massacre, in which 20 children and six adults were killed by a crazed gunman.

Barber, who served as Giffords’ district director, was among those wounded in the Congress on Your Corner shooting on Jan. 8, 2011. He was shot in the face and in the leg.

Team Barber rejected McSally’s calls to condemn the ad.

“Southern Arizonans want to know exactly where both candidates stand on important issues, like keeping guns out of the hands of dangerous criminals and domestic abusers,” Barber spokeswoman Ashley Nash-Hahn said. “Ron Barber supports common sense steps like background checks for gun shows and online sales because stalkers and domestic abusers should not be able to buy guns.”