US Senator John Walsh said his failure to attribute conclusions and verbatim passages lifted from other scholars' work in his master's thesis at the US Army War College was an unintentional mistake caused in part by post-traumatic stress disorder. The apparent plagiarism first reported by The New York Times was the second potentially damaging issue raised this year involving the Democrat's 33-year military career, which has been a cornerstone of his campaign to keep the seat he was appointed to in February, when Max Baucus resigned to become US ambassador to China. Democrats said on Wednesday they remained "100 per cent behind Senator Walsh" in his campaign against Republican congressman Steve Daines. Walsh said that when he wrote the thesis he was suffering from post-traumatic stress disorder from his service in Iraq, was on medication and was dealing with the stress of a fellow veteran's recent suicide. "I don't want to blame my mistake on PTSD, but I do want to say it may have been a factor," the senator said. "My head was not in a place very conducive to a classroom and an academic environment." Walsh submitted his thesis, "The case for democracy as a long- term national strategy", for his Master of Strategic Studies degree in 2007, two years after he returned from Iraq and a year before he became Montana's adjutant general, overseeing the state's National Guard and Department of Military Affairs. The paper includes a series of unattributed passages taken from the writings of other scholars. The first page borrows heavily from a 2003 Foreign Affairs piece written by Thomas Carothers, vice-president for studies at the Carnegie Endowment for International Peace, and a 2009 book by Natan Sharansky with Ron Dermer called The Case for Democracy: The Power of Freedom to Overcome Tyranny and Terror . Sharansky is a former Soviet dissident and chairman of the Jewish Agency for Israel. Dermer is the Israeli ambassador to the United States. All six of the recommendations that Walsh listed at the end of his paper are taken nearly word-for-word without attribution from a Carnegie paper written by Carothers and three other scholars at the institute. One section is nearly identical to about 600 words from a 1998 paper by Sean Lynn-Jones, a scholar at the Belfer Centre for Science and International Affairs, a research institute at Harvard. Lynn-Jones said anyone seeking credit for an academic degree "needs to acknowledge where the material is coming from". "Maybe he unintentionally didn't cite my work, but it's up to the Army War College to determine whether this is acceptable by their standards or not," Lynn-Jones said. The senator said when he wrote the paper, he was seeing two doctors and taking medication to deal with nightmares, anxiety and sleeplessness. He said he had since worked through those issues.