Gansler, who appeared in photos from the party that appeared on social media, said he doesn't recall seeing any drinking, but even if he had, he would not have stepped in.
"Assume for the purposes of this discussion that there was widespread drinking at this party," Gansler said. "How is that relevant to me?"
"The question is, do I have any moral authority over other people's children at beach week in another state? I say no."
Gansler added that his son was not drinking, and he had only stopped by to speak with his son about when they would be leaving Delaware the next morning for a college event in Pennsylvania.
"For better worse, the reality is some kids drink alcohol while they're celebrating senior week," Gansler said. "Was I supposed to serve as police officer? No."
The week-long celebration was put on by a group of parents who paid for a week's stay at a six-bedroom beach house in honor of their sons' graduation from the private Langdon School in Bethesda. Planning documents said there were to be two fathers serving as chaperones each night, no girls behind closed doors and no drinking of hard alcohol.
Gansler said he did not write the rules, but he had discussed them with the other parents and the boys. The rules did not mention drinking beer or wine.
"If anything bad happened, if the kids violated the rules, they'd be sent home," Gansler said. "My guess is... that if someone drank beer, that would not be an offense for which the chaperones would want to send somebody home."
While Delaware does not distinguish between types of alcohol in prohibiting people under 21 from drinking, parents may allow their children to drink at home.
But Gansler has made advocating against underage drinking an important personal cause, and substance abuse prevention experts disagreed with his assessment that he did not have an obligation to step in.
"For any parent to do this is irresponsible," said Michael Gimbel, a former alcohol abuse prevention official for Baltimore County. "But for an attorney general who fought for these laws on the books is even worse."
And Ralph Blackman, the president of Century Council, for which Gansler filmed a public service announcement encouraging parents to prevent their children from drinking, said he was shocked at Gansler's response.
"You can agree, you can disagree with the legal age," Blackman said. But this is "somehow suggesting that it is OK to break the law. It's part of the value systems that go into young people's decision making."