The Clinton campaign, however, said later Thursday that the former secretary of state's effort to join the Marines was "sincere."
Ann Henry, who met Clinton in 1974 after she moved to Fayetteville, said in an interview that she can remember conversations with Clinton and another friend about testing the way the military treated women who were interested in enlisting. They had similar conversations, Henry said, about testing other institutions, too.
"I can remember discussing it, but I cannot give you the details of when and what was said," Henry said. "Hillary was somebody, she was fearless, she would go and do things just to test it out and I can totally see her doing that just to see what the reaction was."
Clinton has never described her visit to the Marine recruiting office in this context.
The story returned to the spotlight this week after Clinton told voters in New Hampshire about once being turned away at a recruiting office in Fayetteville. The story raised questions about why a young lawyer, known for her anti-war views, would try to join the Marines, despite having a new job as a law professor and an upcoming marriage with law school sweetheart Bill Clinton.
Sen. John McCain, R-Ariz., joined in the criticism on Thursday and mocked Clinton on Twitter
A spokesman for the Clinton campaign, after declining to comment for two days, issued a statement Thursday night to CNN that was at odds with Henry's account.
"As she has noted in the past, Hillary visited a Marine recruiter shortly after moving to Arkansas because she was interested in exploring options for serving in the military," the spokesman, Nick Merrill, said. "She did not pursue the idea further and her sole reason for visiting the recruitment center was to determine if there was a suitable opportunity for her to serve in some capacity."
Merrill said Clinton's interest in the Marines "was sincere" and dismissed any criticism as partisan. He added, "it is insulting, but not surprising, that Republicans would attack her for this, too."
But Henry, who is now a retired professor at the University of Arkansas, told CNN that she, Clinton and longtime friend Diane Blair often discussed studying how women would be accepted in various male-dominated occupations.
Henry said the suggestion that Clinton made up the encounter is bogus. She said she believes it was part of a test for how women were treated, rather than an effort to actually serve in the Marines.
"This whole idea that she is fabricating certain things, I am sorry, she has done a lot of things in her life that most women have not done," Henry said. "She was a trailblazer."
Henry said that when Clinton moved to Arkansas in 1974 she was uninterested in appearance and focused on making her life count.
"She was focused on making a difference," Henry said, recalling that the trio -- she, Blair and Clinton -- would regularly talk about policy and ways in which they could test the treatment of women.
Henry chalked Clinton's interest in making a difference to her Methodist upbringing.
"A lot of the times when we were together we talked about the different issues, especially about certain occupations that hadn't been traditionally open to women," Henry said. "I am a lawyer, when I started law school I was one of two women in my class."
Clinton has repeated her Marine anecdote a few times over the years, dating back to at least 1994 when she was first lady. She has never directly answered why a fervently anti-war college student -- who worked on the presidential campaigns of Eugene McCarthy and George McGovern -- would have tried to join the military.
Clinton made the comments at a breakfast on Tuesday
in New Hampshire at a forum called the "Candidate Café," sponsored by WMUR-TV. It was not open to reporters, but a clip of the event was posted on the station's website.
She laughed as she recalled being turned away by a recruiter.
"He looks at me and goes, "Um, how old are you?" Clinton recalled. "And I said, 'Well, I am 26, I will be 27.' And he goes, 'Well, that is kind of old for us.' And then he says to me, and this is what gets me, 'Maybe the dogs will take you,' meaning the Army."
In 1994, she said she also was turned away because of her gender.
"You're too old, you can't see and you're a woman," Clinton said at the time.
While Clinton has never described her visit to the Marine recruiting office as a clandestine exercise, she has frequently talked about going undercover a few years earlier when she worked for the Children's Defense Fund and was part of an investigation into segregated schools in Alabama.
"I was, frankly, posing as a white parent, even though I was a very young lawyer, who was going to be in the area in order to elicit information about what the real intentions were so we could put together a big dossier and submit it to the administration and the IRS to deny charitable exemptions for these segregated academies," Clinton said last month in an interview with The Joe Madison Show on Sirius XM radio.
Blair, who died in 2000, was the closest friend Clinton had in Arkansas. The two taught together at the university in Fayetteville and regularly corresponded as Clinton's life went from small town college professor to first lady.
In the reliably loyal and closely-protective Clinton inner circle, Blair was a power center for most of the former first lady's life. She counseled Clinton during the failed push for health care reform in 1992 and was at her side during Bill Clinton's affair with White House intern Monica Lewinsky.