HELENA, Mont. -

Montana Sen. John Walsh's thesis written for the U.S. Army War College contains unattributed passages that appear to be taken word-for-word from previously published papers.

The Democrat is running to keep the seat he was appointed to in February. Walsh faces Republican U.S. Rep. Steve Daines on Nov. 4.

The New York Times first reported the apparent plagiarism in Walsh's 2007 thesis, titled "The Case for Democracy as a Long Term National Strategy." Walsh submitted the paper in pursuit of a Master of Strategic Studies degree.

Walsh's thesis appears to borrow heavily from a Carnegie Endowment for International Peace Paper written in 2002. One paragraph from the Carnegie paper that offers advice on how to promote democracy in the Middle East is copied verbatim into Walsh's thesis.

Lauren Passalacqua, a Walsh campaign spokesperson, responded with this statement to NBC Montana, “This was unintentional and it was a mistake. There were areas that should have been cited differently but it was completely unintentional. Senator Walsh released every single evaluation that he received during his 33-year military career, which shows an honorable and stellar record of service to protecting Montana and serving this country in Iraq.”

A New York Times interactive graphic breaks down the text of the paper and compares it with the documents Walsh allegedly copied.

We also spoke to Walsh, via phone, who said, "I made a mistake on the paper; I admit that. You know, now I'm going to focus on what's important to Montanans, and that's fighting for jobs, making sure our public lands remain in the hands of Montana and looking after women's health care issues."

It's the second time a portion of Walsh's record has been called into question.

Last year documents showed Walsh had been reprimanded by the Army for using his position as Adjutant General to encourage troops to join the National Guard Association of the United States.

NBC Montana wanted to know if one of Walsh's key supporters thought his military record might be a weakness headed into the November campaign. Justin Barasky is the National Press Secretary for the Democratic Senatorial Campaign Committee, the Democratic Party's chief money-raising organization for senate campaigns.

Barasky called the allegations disgusting and says the committee stands by Walsh 100 percent.

"Take a look at some of the highlights of his career -- Bronze Star for exceptionally meritorious service, August 2005. Praise for his leadership in Iraq, June 2005. He was given an evaluation in 2008 as a consensus builder who models the Army's values, whose honesty and integrity are beyond reproach," Barasky said.

Barasky says the plagiarism accusations are an attack coordinated by Republicans after multiple polls show Walsh gaining points.

Walsh says he was on medication and being treated for post-traumatic stress disorder when he used unattributed work of scholars in his master's thesis.

Walsh told The Associated Press on Wednesday that his "head was not in a place very conducive to a classroom and an academic environment." He was being treated and taking medication for persistent nightmares, anxiety, sleeplessness and the recent suicide of another veteran.

He says he has worked through those issues, though he is still taking antidepressant medication. Walsh says he will consider apologizing to the scholars for lifting their work.