CONCORD, N.H. — A top campaign adviser to Hillary Rodham Clinton resigned, a day after suggesting Democrats should be wary of nominating Barack Obama because his teenage drug use could make it hard for him to win the presidency.
Clinton herself apologized to Obama as they waited to fly to Iowa for a debate.
Obama's campaign sent out a fundraising letter contending that "this kind of attack is becoming a pattern as Clinton's support declines."
Bill Shaheen, a national co-chairman for Clinton and a prominent New Hampshire political figure, had raised the issue of Obama's youthful drug use during a Wednesday interview, published on washingtonpost.com.
"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," Shaheen said in a statement released by the campaign Thursday. "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."
Shaheen, an attorney and veteran organizer, had said much of Obama's background is unknown and could be a problem in November 2008 if he is the Democratic nominee. He said 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 a former New Hampshire 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.
Clinton personally apologized to Obama when they were on the tarmac at Washington's Reagan National Airport Thursday morning, preparing to fly to Des Moines for a debate, according to aides to both candidates.
"Having been on the receiving end of unfair attacks for years, she doesn't think this is what the campaign should be about," said Clinton spokesman Jay Carson. "She told him she wanted to win the presidency, but not through tactics like that."
Clinton's campaign said it had nothing to do with Shaheen's earlier comments.
However, Ned Helms, an Obama co-chairman in New Hampshire, said he saw a pattern after the recent resignations of two Clinton volunteer coordinators in Iowa who had forwarded e-mails raising questions about Obama's religion.
"When you see a pattern of people making statements and the follow-up statement, 'Oh, that wasn't authorized,' it doesn't take a genius to see that there's a thread going on here," Helms said.
And the Obama campaign sent a fundraising e-mail to supporters asking for donations to help fight such tactics.
"The only way to stop these kinds of tired, desperate attacks is to demonstrate very clearly that they have a real cost to Senator Clinton's campaign," campaign manager David Plouffe wrote. "Make no mistake _ this kind of attack is becoming a pattern as Clinton's support declines."
Obama wrote about his teenage drug use 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.
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.