Montana Democrat John Walsh dropped his bid to retain his U.S. Senate seat on Thursday, saying recent plagiarism allegations had proved too much of a distraction.
Walsh, a decorated Iraq war veteran, is under investigation for copying much of a paper he submitted for a master's degree at the U.S. Army War College. The college and the Defense Department are investigating the matter.
"The 2007 research paper from my time at the U.S. Army War College has become a distraction from the debate you expect and deserve," Walsh said in a statement. "I am ending my campaign so that I can focus on fulfilling the responsibility entrusted to me as your U.S. senator."
He said he would serve out the rest of his term, which ends in January.
Walsh had faced immense backlash from Republicans -- along with Democrats -- after the New York Times reported in July that he had lifted several excerpts for his final paper for his master's degree. The outrage only increased when he told the Associated Press that his failure to attribute the work of others was due in part to post-traumatic stress disorder. He quickly backed away from that excuse and apologized.
His history of military service had been considered a strength in the conservative state when Democratic Gov. Steve Bullock appointed him in February to replace longtime Sen. Max Baucus, who became U.S. ambassador to China.
The plagiarism allegations undermined those credentials.
"This was always a tough race for Democrats, given the national electoral environment and the environment here," David Parker, a professor of political science at Montana State University, told the Los Angeles Times. "Now it's amplified. Democrats need to select a someone who has strong name ID all around the state and who can raise money fast."
The state Democratic Party will nominate a new candidate to run against Rep. Steve Daines, the GOP nominee and front-runner.
Parker said the front-runners for the Democratic nomination could be former Gov. Brian Schweitzer or Nancy Keenan, former president of NARAL Pro-Choice America. Schweitzer tweeted that he would not seek the nomination, however.
"It's going to be very, very tough for Democrats to retain this seat," Parker said.
Republicans need a net gain of six seats to take control of the Senate, and Montana is one of three they have counted on. The other two are in West Virginia and South Dakota, where Sens. John D. Rockefeller IV and Tim Johnson are retiring.
The GOP also appears increasingly confident in Iowa, where the Democratic candidate, Rep. Bruce Braley, has stumbled repeatedly. But Democrats hope that their incumbents in four other closely contested races, in North Carolina, Louisiana, Arkansas and Alaska, can pull through.
President Obama lost all four of those states in the 2012 election, but polling has shown each of the incumbent senators continuing to run competitive races.
In Montana, the state Democratic Party lauded Walsh as he left the race.
"Sen. Walsh's life has been and continues to be service to our nation and all Montanans," Democratic Party Chairman Jim Larson said in a statement. "From 33 years in the National Guard, to serving as lieutenant governor to his time in the U.S. Senate, John Walsh has sacrificed significantly for our country and is to be commended."