Montana Democratic Sen. John Walsh is dropping out of his Senate race after being dogged by allegations of plagiarism, potentially boosting Republicans' chances of picking up the seat in November.
The senator made the announcement late Thursday in a message to supporters. Walsh said the plagiarism claims have become a "distraction" from the issues.
"I am ending my campaign so that I can focus on fulfilling the responsibility entrusted to me as your U.S. Senator. You deserve someone who will always fight for Montana, and I will," he said in the message.
Calls for Walsh to bow out have grown louder following accusations that first surfaced last month that he plagiarized part of a paper he submitted for his master's degree in 2007.
Three of Montana's largest newspapers recently called for him to withdraw his candidacy, while others have demanded he apologize or forfeit his master's degree.
The decision comes as a U.S. Army War College investigation is set to begin Aug. 15 into the paper that Walsh previously said unintentionally contained wrongfully cited passages. Walsh also had until Monday to drop out of the race.
His decision to withdraw from the November election allows the Montana Democratic Party to hold a nominating convention to choose a replacement candidate before the Aug. 20 deadline to do so. The convention will be composed of Democratic leaders from each county's party committee, along with federal and statewide elected officials and the party's executive board. They will nominate potential candidates who will have a chance to speak before the convention before voting gets underway.
The nominee who receives a majority of votes will be selected as the replacement candidate, according to the party's rules.
Walsh's decision is likely to give a boost to Republican Rep. Steve Daines, who is giving up his House seat to run for Senate. Republicans need to gain a net of six seats in the election to take control of the Senate, and Walsh had faced a tough race against Daines before the plagiarism allegations.
Walsh had already announced his candidacy for the seat when Gov. Steve Bullock appointed him in February to replace Max Baucus, who resigned from the Senate to become ambassador to China. Republicans blasted Bullock's appointment of his lieutenant governor as a political move designed to gain an advantage in the elections.
The New York Times revealed the extensive use of unattributed material in Walsh's paper about the spread of democracy in the Middle East. Walsh originally called it an "unintentional mistake" and told The Associated Press part of the blame may lie in his being treated for symptoms of post-traumatic stress disorder following his deployment in Iraq.
He later said he was not blaming PTSD for his mistake.
Walsh is the only U.S. senator who served in the Iraq war. He capped a 33 years in the Montana National Guard, his career rising to state adjutant general before he took his first elected office in 2013 as Bullock's lieutenant governor in 2013. Walsh received the Master of Strategic Studies degree from the war college at age 47, a year before he became adjutant general overseeing the Guard and the state Department of Military and Veterans Affairs.
The Associated Press contributed to this report.