(CNN) - Connecticut Attorney General Richard Blumenthal acknowledged Tuesday that he has not always accurately described his military service during the Vietnam War - a decades-old biographical question that is suddenly threatening to derail his frontrunner's campaign for the U.S. Senate.
"On a few occasions I have misspoken about my service and I regret that and I take full responsibility," Blumenthal said while surrounded by Vietnam veterans at a news conference in West Hartford. "But I will not allow anyone to take a few misplaced words and impugn my record of service to our country.
"I served in the United States Marines Corps Reserve and I am proud of it," he said. Any mischaracterization was "absolutely unintentional."
A New York Times story released earlier in the week alleges that Blumenthal, a Democrat, lied about serving in Vietnam. The story says Blumenthal never served in that war, even though the candidate has claimed he
did in several speeches before veterans groups and military families.
It states that Blumenthal obtained at least five military deferments from 1965 to 1970 and took repeated steps that enabled him to avoid going to war. In 1970, the New York Times says, he enlisted in the Marine Reserve and landed a coveted spot in a unit in Washington.
The story also claims that it appears Blumenthal did nothing to correct numerous media profiles that described him as a Vietnam veteran.
Blumenthal ripped into the Times story, saying that there is "virtually no mention in that article" of the six years he spent in the Marine Reserve. The story "denigrates" service in the Reserve, he argued, and wrongly implies that he used special favors to get into it.
"I looked (the Reserve) up in a phone book," he said.
Sen. Robert Menendez of New Jersey, the point man for Democratic Senate campaign efforts this year, sought to downplay the story, saying Tuesday that Blumenthal "has been an incredible advocate for veterans."
"I think he's corrected the record in the past," Menendez said. "And I think his actions as it relates to standing up for veterans over a long period of time speaks volumes of where his heart and his actions are."
Menendez said Democratic leaders will continue to back Blumenthal's bid to fill the seat held by retiring Sen. Chris Dodd. Dodd himself said Tuesday that Bloomberg is "the most honorable of people."
"My support for him is unwavering," Dodd added.
Blumenthal's political opponents, however, were quick to go on the attack.
"Mr. Blumenthal owes the people of Connecticut, and particularly its veterans, a thorough explanation for the very serious questions that have been raised over what appears to be a long history of dishonest statements," said National Republican Senatorial Committee spokesman Brian Walsh.
The campaign for Republican candidate Linda McMahon claimed credit Tuesday morning for giving the New York Times a video of a speech in Norwalk, Connecticut, in which Blumenthal allegedly said he served in Vietnam.
Republican candidate Rob Simmons released a statement Monday night saying he was "deeply troubled" by the allegations.
"Too many have sacrificed too much to have their valor stolen in this way. I hope Mr. Blumenthal steps forward and forthrightly addresses the questions that have arisen about this matter," he said.
One of the sources in the New York Times story, however, said Tuesday that she had been misquoted in the article.
Jean Risley, who chairs the Connecticut Vietnam Veterans Memorial Inc., was mentioned in the story as describing Blumenthal's comments at the dedication of the Connecticut memorial: "He said, 'When we came back, we were spat on; we couldn't wear our uniforms.'"
The story went on to say that Risley "later telephoned the reporter to say she checked into Mr. Blumenthal's military background and learned that he had not, in fact, served in Vietnam."
Risley said, however, that Blumenthal never told her he went to Vietnam. "I never heard him say that," she said. "He wasn't referring to himself."
She characterized Blumenthal's comments as descriptive of Vietnam veterans as a group rather than any single person's individual experience, including his own.
"He did misquote me," she said of the Times reporter. "They added stuff I didn't say. I never checked into Blumenthal's military background."
Risley later appeared at Blumenthal's news conference, repeating her assertion that she "never once heard him say" that he had served in Vietnam. But "I did hear him say how passionately he felt about our veterans and how we had to honor them," she said.
Blumenthal, Connecticut's attorney general for the past two decades, announced his candidacy January 6, hours after Dodd, a five-term senator, announced that he would not run for re-election in November. Dodd had been considered one of the most vulnerable Democrats in 2010.
A Quinnipiac University survey conducted in March indicated that Blumenthal was up by more than 2-to-1 margins over all three of his possible Republican opponents.
The Connecticut Democratic Party's nominating convention begins in Hartford on Friday.
Updated: 4:16 p.m.
– CNN's Ted Barrett, Alan Silverleib and Allan Chernoff contributed to this report.