The Hillary Clinton adviser who in published statements warned Barack Obama that his admissions of past drug use could haunt him on the trail resigned Thursday, shortly after Clinton herself personally apologized to Obama.

The campaign has accepted the resignation of Bill Shaheen, the New Hampshire co-chairman, and released Shaheen's statement Thursday.

"I would like to reiterate that I deeply regret my comments yesterday and say again that they were in no way authorized by Senator Clinton or the Clinton campaign. Senator Clinton has been running a positive campaign focused on the issues that matter to Americas families," he said in the statement. "I made a mistake and in light of what happened, I have made the personal decision that I will step down as the Co-Chair of the Hillary for President campaign. This election is too important and we must all get back to electing the best qualified candidate who has the record of making change happen in this country. That candidate is Hillary Clinton."

Clinton personally apologized to Obama Thursday morning on the tarmac en route from Washington, D.C., to a debate in Iowa. It was one of several steps in the cleanup effort by the Clinton campaign to minimize damage from the adviser's remark, published on The Washington Post Web site on Wednesday.

"Senator Clinton personally apologized to Senator Obama this morning, and reiterated that this was not anything that came from the campaign or that we condone," Clinton's New Hampshire spokeswoman Kathleen Strand said in a statement.

Shaheen previously issued an apology after Clinton spokesman Phil Singer said the remarks "were not authorized or condoned" by the campaign.

In the Post article, Shaheen, an attorney and veteran organizer, said much of Obama's background is unknown and could be a problem in November 2008 if he is the Democratic nominee. He said the Republicans would work hard to discover new aspects of Obama's admittedly spotty youth

"It'll be, 'When was the last time? Did you ever give drugs to anyone? Did you sell them to anyone?"' said Shaheen, whose wife Jeanne is the state's former governor and is running for the U.S. Senate next year.

"There are so many openings for Republican dirty tricks. It's hard to overcome," Shaheen said.

Obama campaign manager David Plouffe said in response to Shaheen's remarks:

"Hillary Clinton said attacking other Democrats is the fun part of this campaign, and now she's moved from Barack Obama's kindergarten years to his teenage years in an increasingly desperate effort to slow her slide in the polls. Senator Clinton's campaign is recycling old news that Barack Obama has been candid about in a book he wrote years ago, and he's talked about the lessons he's learned from these mistakes with young people all across the country. He plans on winning this campaign by focusing on the issues that actually matter to the American people."

Obama wrote about his teenage drug in his memoir, "Dreams from My Father." His rivals have largely remained silent on the subject.

"Junkie. Pothead. That's where I'd been headed: the final fatal role of the young would-be black man," Obama wrote. Mostly he smoked marijuana and drank alcohol, he wrote, but occasionally he would snort cocaine when he could afford it.

Speaking to Manchester high school students earlier this month, Obama said he was hardly a model student and had experimented with drugs and alcohol.

"You know, I made some bad decisions that I've actually written about. You know, got into drinking. I experimented with drugs," he said. "There was a whole stretch of time that I didn't really apply myself a lot. It wasn't until I got out of high school and went to college that I started realizing, 'Man, I wasted a lot of time."'

New polling shows Clinton and Obama basically tied in New Hampshire. A CNN-WMUR-TV poll conducted by the University of New Hampshire shows Clinton at 31 percent support, Obama at 30. The same poll had Obama trailing by 20 points in September.

Clinton's campaign has distributed its first flier that criticizes Obama's health care plan for leaving 15 million people without insurance. TV ads following the same theme also have been prepared.

"This is not the time to go back to the same old politics of, 'now I'm going to smack you over the head with a baseball bat and call into question your character,"' Obama co-chairman Ned Helms told reporters in a conference call earlier on Wednesday, decrying what he said was Clinton's negative campaign.

"I think it will backfire on them. I think they had instinctively good judgment to say Hillary Clinton would not take personal attacks. But once polls showed them losing out on the positive argument to Barack Obama, they have chosen to go negative."

FOX News' Aaron Bruns and The Associated Press contributed to this report.