Doug Gansler

This photo -- obtained by ABC News -- was taken at a party attended by Doug Gansler. (October 24, 2013)

Maryland Attorney General Douglas F. Gansler said Thursday that showing up at a "beach week" party of teenagers and not investigating whether there was underage drinking was "a mistake that I made."

"Perhaps I should have assumed there was drinking going on, and I got that wrong," Gansler said.

He said he stopped only briefly at the party in Delaware last June to see his son and left without asking the teenagers — including shirtless boys and a girl dancing on a tabletop — about the red plastic cups scattered around the party.

"There could be Kool-Aid in the red cups, but there's probably beer in the red cups," he told reporters.

Gansler, Maryland's chief law enforcement officer and a candidate for governor, held a news conference Thursday after The Baltimore Sun published a photo that showed him at the center of the party in South Bethany, along with his comments that he had no "moral responsibility" to intervene.

The image and Gansler's assertion made national news Thursday. Gansler has been an outspoken advocate for stricter laws against underage drinking.

The episode delivers the latest blow to Gansler's campaign for the Democratic nomination next year.

"Can things get any worse?" asked Matthew Crenson, professor emeritus of political science at the Johns Hopkins University.

Gansler has faced allegations that he ordered the state troopers on his security detail to drive recklessly and speed, failed to pay for traffic tickets and described his chief Democratic political rival Lt. Gov. Anthony G. Brown, an African-American, as relying on his racial heritage to get elected.

In each case, analysts said, the damage was amplified by Gansler's response.

"He's just had one mistake after another," Crenson said. "I just can't believe people are going to put up with this."

At the news conference in front of his Silver Spring campaign headquarters, Gansler dismissed suggestions that his bid for governor had faltered.

"We're in it. We're going to win it," Gansler said. "The people of Maryland, they want somebody with the character, judgment, record, vision, authenticity, who is genuine and going to make the best Maryland. We're fine."

At the same time, Gansler reversed some of his comments about his responsibility at the party. Campaign spokesman Bob Wheelock said the change came "after reflection."

The party came at the end of a weeklong trip Gansler and other parents helped organize and finance for a dozen boys who had just graduated from the Landon School, a private school for boys in Bethesda.

Written rules given to the teens who were staying at the house for the week forbade drinking "hard liquor," but included no such instructions about beer.

On Thursday, Gansler described himself as a father facing "the tension for all parents" of teenagers about to leave for college.

"How much do you let them go? How much do you sort of rein them in?" he said. In hindsight, he said, "I should have assumed that there was drinking."

Gansler said his son wasn't drinking at the party.

The report sparked a vigorous debate on Baltimore talk radio about the responsibilities of parents to monitor the alcohol use of their underage children. Former Ravens owner David Modell called in to WBAL-AM to demand Gansler's resignation.