Sen. John Walsh, D-Montana, said Friday that the United States Army War College has revoked his master's degree after investigating allegations that he plagiarized much of a thesis he submitted to earn his degree.

"Though I disagree with the findings made by the War College, I accept its decision with great humility and respect for the U.S. Military," Walsh said in a statement. "I apologize to all Montanans for the plagiarism in my 2007 paper, and I am prepared to live with its consequences."

The plagiarism, first reported by the New York Times in August, occurred in a paper on Middle Eastern politics Walsh submitted to the college in 2007, when he was part of a 10-month graduate studies program.

In the paper, Walsh lifted large passages from other sources without attribution, including several policy recommendations at the end of the paper that were stolen from a paper by academics at the Carnegie Endowment for International Peace.

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Other passages were copied from a paper written by a scholar at Harvard University.

After the allegations first surfaced, Walsh insisted the mistake was unintentional, saying he was suffering from symptoms of post-traumatic stress disorder at the time he wrote the paper. He said he did not want to blame PTSD for the error, but added that it "may have been a factor."

Just days after the accusations went public, the college said it would conduct its own investigation into the matter.

In short order, the scandal forced Walsh to abandon his plans to seek election to a full term six-year term in the Senate. He was first appointed to the chamber in February to replace departing Democratic Sen. Max Baucus, who was appointed the U.S. Ambassador to China.

Before the allegations of plagiarism, Walsh was considered one of the most endangered Democratic incumbents. His seat is now considered an almost-certain pickup for Republicans, who need a net gain of six seats to seize the majority.