Washington (CNN) Sen. Heidi Heitkamp issued a personal apology on Tuesday after her campaign identified some women as survivors of abuse in an ad without their knowledge or consent.

The misstep has led some women misidentified in the ad to decry the Democratic candidate and question how their names landed on the list, with one group of women saying they are seeking "a lawyer who will take our case" because the ad has "interfered with, or downright ruined, our lives."

The Heitkamp campaign, looking to slam Rep. Kevin Cramer, her Republican opponent, for suggesting "tough people" do not identify with the national conversation around sexual assault and the treatment of women, ran an open letter to Cramer to show him "what prairie tough looks like."

The letter featured over 120 names at the bottom, but several women have come forward to say they were either included without their permission or were not survivors of "domestic violence, sexual assault, or rape," as specified in the letter.

In response, Heitkamp admitted the mistake and said she was "personally apologizing" to each person impacted.

"We 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," Heitkamp said in a statement. "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."

Heitkamp's bid for re-election in a state that President Donald Trump won by 36 percentage points in 2016 has been an uphill climb from the start, despite the fact that Cramer has made a number of comments that have caused Republicans in Washington to cringe. A series of recent polls have found Cramer leading Heitkamp, including a Fox News survey that found him with a 12-percentage-point lead -- 53 to 41.

After Heitkamp spent hours on Tuesday trying to clean up the mistake, Shylah Forde, Megan Stoltz and Alexandria Delzer, three of the misidentified women, provided CNN with a statement from a group they said represents over a dozen women who landed on the list without their consent. They declined to provide the names of all the women who signed on to the statement.

"Heidi Heitkamp's political agenda has interfered with, or downright ruined, our lives," they wrote. "Survivors of assault who had taken care to avoid the subject were suddenly bombarded by questions asking them to explain to their loved ones why their name appeared on this list. Women who have never been assaulted spent the day reassuring loved ones of their safety."

The group of women went on to say that their "privacy was violated on this day" so they have begun to "search for a lawyer who will take our case."

A Heitkamp spokeswoman, asked about the legal threat, referred CNN to the senator's earlier comments.

The reaction to the ad was started by Kady Miller, one of the women identified at the bottom of the open letter.

"I don't even support Heidi Heitkamp and I am not a domestic abuse survivor," she wrote on Facebook with a photo of the ad.

Miller, reached by CNN on Tuesday, said that she was not a Heitkamp supporter and did not believe a personal apology from the senator would make amends.

"What's done is done and I don't think she can even get out of this one or fix it in any way," she said. "Our names have already been published in multiple newspapers."

Lexi Zhorela, another woman named on the list, also responded that she did not give permission to have her name published.

"I am beyond furious," she wrote. "There are so many woman (sic) in this list including myself that have been victims of sexual adult (sic) -- and more of us probably didn't want our name (sic) to be spread across the news for everyone to see."

She added: "I will not stand for this."

Zhorela, in an interview with CNN, said that she and "many other women on this list" were "very publicly humiliated on more than one level."

She added that a representative from the campaign has contacted her and said she will receive a personal phone call apology from the senator, but that the call has yet to happen.

"That doesn't really do justice to the hurt this has caused not just me but many women that were wrongfully put in this situation," she said.

Zhorela said she was a liberal and had planned to back Heitkamp.

"That has changed," she added.

Another woman whose name incorrectly appeared on the letter but asked to remain anonymous called the ordeal "humiliating."

"I'm not even a survivor and my name was included in the ad," she said. "I had family and friends calling me all concerned. It was humiliating."

Other women who posted on Facebook did not respond when CNN contacted them.

A Heitkamp aide told CNN that the campaign worked with victims' advocates in North Dakota on the ad and the list of women.

Heitkamp, in response to the controversy, blanketed the radio waves with a series of interviews on Tuesday. In one emotional interview with WZFG, Heitkamp said that the criticism of her campaign was "legitimate" and that she took responsibility for the issue.

I feel "horrible and mad and angry and furious and ready to tell someone 'what were you thinking,' why is this happening, how could you have been this irresponsible," she said. "I have gone through all of that exactly how you set it out, 'what if this was my daughter, what is this was my son, how would I react to this?'"

She added: "I don't think anyone is perfect in the world and sometimes when you are on a big stage you can make big mistakes, and I think our campaign made a big mistake and we need to own it and we need to fix it."

Heitkamp and her team are now working to determine who provided the unauthorized names, with the senator telling one radio host that there "will, in fact, be consequences."

Kylie Oversen, the former North Dakota Democratic Party chairwoman and a candidate for North Dakota tax commissioner, helped in the process, she told CNN on Tuesday, but said that she provided "fewer than 10 names... and they were all individuals that authorized me to use their name."

Oversen, who also signed the letter, said that there were "many people who were just helping to reach out to leaders in the community and contact people who would be willing to sign."

Republicans quickly highlighted the story, with Cramer calling the ad a "revictimization of victims," according to local media.

"Eager to save her failing campaign, Heidi Heitkamp has stooped to a new low," Michael McAdams, a spokesman for the National Republican Senatorial Committee said in an email.

"This is another example of Heidi Heitkamp exploiting whoever she can for political gain," said Jake Wilkins, Communications Director for the North Dakota Republican Party. "With a campaign built on lies, misinformation, and manufactured controversy, it's no wonder Heitkamp is the most vulnerable Senator in the country."