Gansler told reporters at a news conference that he stopped by the June 13 party in South Bethany, Del., to meet with his 19-year-old son and discuss travel plans for the next day. A photograph obtained by The Baltimore Sun and published Thursday shows Gansler amid a group of partying teens. Some of the teens are dancing and several plastic cups are visible.
Gansler said that while there was loud music, he didn't see any drinking. He said he left soon after talking with his son and saw no reason to call police.
"I think I probably should have done more," Gansler said Thursday afternoon at the news conference outside his campaign headquarters.
Gansler's reaction shifted from earlier comments to The Sun, in which he said if he had seen drinking, it wouldn't have been his responsibility to intervene.
Gansler starred last year in a public service announcement for The Century Council, an organization sponsored by the liquor industry that fights drunken driving and underage drinking. In the 30-second video spot, Gansler says parents are the leading influence on their kids' behavior when it comes to alcohol, noting, "It's never too early to talk to your kids about smart ways to say, 'No.'"
Council CEO Ralph Blackman said he expects the spot will be withdrawn from the organization's YouTube channel.
"We talk a lot about the mixed messages that parents sometimes send to kids. It's a bit of a mixed message for us" to have Gansler's PSA available while his actions are under scrutiny.
Gansler's campaign for the Democratic gubernatorial nomination has been going through a rough patch.
The Washington Post published a story last week about Maryland State Police describing Gansler as directing troopers assigned to protect him to bypass traffic by driving on the shoulder and presenting other safe-driving concerns.
Gansler responded by calling the commander of the state police's executive protection section a "henchman" of Democratic Gov. Martin O'Malley and Democratic Lt. Gov. Anthony Brown, who is running against Gansler for the party's nomination. Gansler's remarks brought a rebuke from state police.
The nominating race has been highly competitive because O'Malley is barred by term limits from seeking a third term in the heavily Democratic state. It got off to an early start his year, partly because the primary has been moved up from September to June.
Associated Press writer Matthew Barakat in McLean, Va., contributed to this report.