(CNN) - Republican Linda McMahon is trying to seize the offensive in the hotly contested Connecticut Senate race, unveiling a new ad slamming Democratic state Attorney General Richard Blumenthal over distortions in his Vietnam service record.
The new ad, which will air statewide, made its on-line debut only hours before the two candidates are scheduled square off in their first debate. It raises questions about Blumenthal's credibility as a politician.
"Would you lie about serving in a war?" the narrator asks. "Dick Blumenthal did, again and again. ... If he lied about Vietnam, what else is he lying about?"
The ad shows Blumenthal in Norwalk, Connecticut, in 2008 saying, "we have learned something very important since the days that I served in Vietnam."
It also displays a clip of him in Bridgeport in 2003, telling a crowd, "when we returned (from Vietnam), we saw nothing of this gratitude."
In May, the New York Times reported that Blumenthal had repeatedly distorted his military service record. A Times article alleged that Blumenthal lied about serving in Vietnam and said that he never served in that war, even though Blumenthal claimed he did in speeches before veterans groups and military families.
A day after the release of the article, Blumenthal acknowledged he had not always accurately described his military service in Vietnam. He served in the Marine Corps Reserves during the Vietnam War, and was stationed stateside.
Blumenthal said he mistakenly said he served "in" Vietnam rather than "during" Vietnam in his previous speeches. He said in a statement that "at times when I have sought to honor veterans, I have not been as clear or precise as I should have been about my service in the Marine Corps Reserves."
The revelation helped transform what was expected to be an easy Democratic win into a tight contest. A Quinnipiac University survey released last week showed McMahon trailing Blumenthal 49 to 46 percent among likely voters, with four percent undecided. Blumenthal's three-point advantage was within the poll's sampling error, and down from a six-point margin in a Quinnipiac survey conducted earlier in September.
Blumenthal Campaign Manager Mindy Myers nonetheless dismissed the latest ad as "another desperate attack from a losing campaign with nothing to say."
"Linda McMahon's money can't buy Dick Blumenthal's genuine record of standing up and fighting for the people of Connecticut," Myers said in a statement.
McMahon and Blumenthal are campaigning for the right to retiring Democratic Sen. Chris Dodd's seat. Dodd, who was first elected to the Senate in 1980, announced earlier this year that he would not seek another term in office.