Sen. Heidi Heitkamp of North Dakota, the most endangered Senate Democrat in next month's midterm elections, apologized Tuesday for a newspaper ad that included names of victims of domestic violence, sexual assault or rape without their permission.

The ad was fashioned as an open letter to Rep. Kevin Cramer, Heitkamp's Republican opponent, criticizing comments he made during the confirmation process for Supreme Court Justice Brett Kavanaugh.

In a statement Tuesday, Heitkamp said that her campaign "recently discovered that several of the women's names who were provided to us did not authorize their names to be shared or were not survivors of abuse."

"I deeply regret this mistake and we are in the process of issuing a retraction, personally apologizing to each of the people impacted by this and taking the necessary steps to ensure this never happens again," the statement said.

The ad included names of 127 women. It was not clear how many names were erroneously included or how they came to be part of the newspaper ad.

After publication of the ad, several women whose names were included spoke out on social media.

Lexi Zhorela of Bismarck wrote on Facebook that she was "beyond FURIOUS." She said many women on the list, including her, "didn't want our name spread across the news for everyone to see" and risked retribution from a prior rapist or boyfriend who beat them.

Kady Miller, also of Bismark, wrote on Facebook: "A lot of these people listed, including me, did not give anyone permission for our names to be posted. I don't even support Heidi Heitkamp and I am not a domestic abuse survivor. Should this even be legal?? Using people's names as part of your campaign??"

The Heitkamp ad came in response to Cramer's characterization of the #MeTo0 movement as a "movement toward victimization." He spoke against the backdrop of the controversy over the nomination of Kavanaugh, who faced decades-old allegations of sexual misconduct that he vigorously denied.

Heitkamp voted against Kavanaugh's confirmation while Cramer supported the nomination.

"We are here to let you know that you are wrong - this is not 'a movement toward victimization,' it's about being a survivor," said the open letter in the ad.

Cramer told the Associated Press that he considered the mistakes in Heitkamp's ad "a revictimization of victims."

"This is what happens when desperate people do things for their own personal political gain," he said. "She proved a point that her personal politics matter more than someone's personal pain."