Bush enrolled in the Guard in his home state of Texas in 1968, and transferred to a guard unit in the southern state of Alabama four years later so he could help in the political campaign of a friend of his family.
But there are unexplained gaps in Bush's military record, making it unclear whether he served as he was required to do. Some in the Alabama Guard say they do not remember him. One, Robert Mintz, appears on the television advertisement being aired by Texans for Truth.
"I heard George [W.] Bush get up and say, 'I served in the 187th Air National Guard in Montgomery, Alabama.' Really, you know, that was my unit, and I don't remember seeing you [Bush] there," Mintz said. Mintz has since said that it is possible that Bush was there even though he didn't see him.
But if Bush shirked his duty, how could he have been granted an honorable discharge? Bush's critics attribute that to the influence of his father, George Bush, who had earlier served as a member of Congress representing a district in Texas and who eventually became president in 1999.
In fact, it was that influence that got the younger Bush into the Air National Guard in the first place, according to Ben Barnes, who at the time was the speaker of the Texas House of Representatives. Barnes told the U.S. television network CBS that he personally ensured positions in the guard for hundreds of sons of prominent Texans, including Bush.
At the time, enrolling in a National Guard unit was a way to perform military service without active combat duty in Vietnam. Today, National Guard troops are sent into combat in Iraq, but during the Vietnam War, combat troops were supplied by a military draft.
In an interview with CBS News, Barnes said, "Those that could get into the reserves or those that could get in the National Guard -- chances are, they would not have to go to Vietnam."
Meanwhile, CBS cited documents indicating that Bush did not measure up to the standards set for him in the Air National Guard. One Guard official said he was under pressure to "sugar-coat" Bush's evaluation -- rate his performance as better than it actually was. Questions are now being raised about the authenticity of some of these documents, however, which appear to have been written on personal computers, which of course did not exist in the early 1970s.
Dan Bartlett, the White House communications director, said the documents reveal nothing new. He called the airing of the documents and statements by Barnes "dirty politics," noting that they came 55 days before the presidential election. He also pointed out that Barnes is a major fundraiser in Texas for Kerry.
Kerry reacted much the same way in the face of a spate of advertisements during August that questioned whether he had truly earned the medals he received for valor and wounds during his service in Vietnam. Polls show that his standing suffered as a result.
At the beginning of August, Kerry and Bush were in a dead heat in the race for the presidency. Now Bush has taken a lead. It is too early yet to see whether the new anti-Bush ads will have an effect on the president.
In fact, the attacks on either side probably will have no effect on the race, according to Allan Lichtman, a professor of U.S. history and politics at American University in Washington.
Lichtman said this is good, because attack ads about events of three decades ago should not distract voters from the issues they face today.
"It is a sad commentary on the state of American politics that the urgent issues that really matter for our future are being shunted aside," Lichtman said. "No one is going to vote one way or the other because of any of these arguments. As always, it's going to be the big picture that decides this election: the economy, foreign policy, social unrest, not this back-and-forth character assassination."
Those who attack Kerry and Bush, however, say their stands are relevant because they focus on whether either of the two men has the character to lead the country. Lichtman agrees that character is important, but wonders whether the actions of a man in his 20s really are relevant in his middle age.
"I don't think character is irrelevant, but I do think going back 30, 35 years probably is irrelevant," Lichtman said. "People fundamentally change over the decades. And while it's marginally relevant, there are such urgent matters to be dealt with that it's shameful that we should be dealing with something so far on the fringes of what matters."