With two more debates scheduled this month, the top three GOP campaigns intensified efforts to undermine their opponents -- even as they all claimed to be running positive campaigns.

Arizona Sen. John McCain announced that more than a dozen supporters of the Texas governor had switched to his campaign after Thursday night's nationally televised debate -- the first session attended by Bush.

Bush holds wide leads over the GOP field in state polls across the country, except in this first primary state, where McCain has closed the gap. Forbes is mired in the single digits in most surveys.

Post debate, Forbes rejuvenated questions about Bush's past after the governor zinged him about a 1977 article he wrote on Social Security. The column suggested the retirement age should be raised.

Bush, who was 31 years old and working in an entry-level oil industry job in 1977, has refused to directly answer questions about whether he has used illegal drugs, except to say he has not since 1974. He has said, however, "I did some irresponsible things when I was young and irresponsible."

Forbes mocked the line to make the point that he no longer believes the retirement age should be raised. "When I was young and irresponsible, I was young and irresponsible and, unlike some, I grew from that initial position and clearly some are still stuck in it," he said.

"At least you knew what I was doing in my youth. I was writing magazine columns. Others haven't been so forthcoming about what they were doing," Forbes said.

Bush wouldn't say if he thought Forbes was going negative -- as critics say he did in 1996 against the eventual GOP nominee Bob Dole -- but Bush suggested such tactics weren't wise. "I think the Republican party is anxious for there to be a solid clean campaign on issues," Bush said.

At the McCain news conference, one after another, new backers of the senator suggested that Bush is shallow, yoked to the political establishment, over-coached and immature.

"Is that what I want for president?" asked Leona Dykstra, identified as a former member of Bush's steering committee.

McCain, who exchanged kind words with Bush during the debate, said he did not share his new supporters' views, but added, "I appreciate the comments they're making." He said Bush is qualified to be president.

Still, McCain's advisers were giddy over what the campaign-switchers had to say, even as they denied knowing in advance the details of their problems with Bush.

"It ain't a whisper campaign that the McCain campaign is running," said campaign manager Rick Davis. The Bush campaign has denied accusations that its supporters are spreading rumors about whether McCain is fit for office in light of his temper and Vietnam POW experiences.

Bush, fielding a wide range of questions in his news conference, said he wasn't worried about whispers that he lacks the intellect to be president, calling it "the empty-suit syndrome." If voters have doubts, "Send them to Texas. People in Texas know I know how to lead," he said.

Forbes went farther than he normally does in discussing Bush's personal life. Moments after the debate, the publisher joked in a news conference, "When I was a young and irresponsible youth I was writing magazine articles. Enough said."

"It was a throw away line that got a chuckle (Thursday night). That's all there was to it," Forbes said in a telephone interview Friday.

"It is out of bounds to talk about somebody's personal life," he said, insisting he didn't cross the line. "... I'm not going to ask about it, mention it, talk about it. It's out of bounds."

Forbes quipped, "The lesson here is I won't be making a living writing one-liners for Jay Leno."

Aides to Gov. Bush were blunt in their criticism of Forbes. "Desperate candidates do desperate things," said Bush's chief spokesman, Karen Hughes.

Forbes spokesman Greg Mueller shot back at the Bush campaign, saying, "I guess they better start doing desperate things because they are in real trouble in New Hampshire and Iowa."

Mueller said Forbes was justified in drawing the comparison between their "youthful irresponsibilities" because Bush delved 22 years into Forbes' past in the debate.

"The candidate who said what he did in the '70s is off limits is passing out material that Steve Forbes wrote in the '70s," said Mueller said.