The questions elicited differences among the candidates on a variety of issues. Mr. Romney tangled with Mr. McCain over whether waterboarding should be defined as torture. Mr. Romney said that if the Supreme Court overturned Roe v. Wade and Congress passed legislation outlawing all abortions nationwide, he would sign it; Mr. Giuliani said he would not, saying the decision about abortion should be up to each state. Mr. Tancredo, Mr. Huckabee, Mr. Romney and Mr. Giuliani said they all supported or had signed a pledge put forward by an anti-tax group, Americans for Tax Reform, never to raise taxes; Mr. McCain and Mr. Thompson said they would only make pledges to the American people and Mr. Hunter said that raising taxes could be necessary in a national emergency.

The debate provided an odd juxtaposition: eight dark-suited male candidates addressing the concerns of a more youthful, diverse group of videographers that included a guitar strummer, Uncle Sam, a corn-cob eating questioner in a T-shirt, and even beltway insider and anti-tax activist Grover Norquist.

And the candidates themselves submitted videos, with Fred D. Thompson’s perhaps the most barbed: it cited “flip flops” by Mr. Romney on abortion rights, and Mr. Huckabee on raising taxes. Mr. Giuliani’s video playfully told how he had tackled the perils of New York City, taking on King Kong and even reducing snowfall.

Mr. Thompson, the actor and former Tennessee Senator, used the immigration issue to score points against both Mr. Romney and Mr. Giuliani. He noted that Mr. Romney had once supported a similar immigration bill to the one he opposed as a presidential candidate. “Now he’s taken another position, surprisingly,” he said, drily alluding to some of the other positions on which Mr. Romney has changed, such as his switch from supporting abortion rights to opposing them.

And he questioned the wisdom of Mr. Giuliani’s attack on the illegal immigrants that Mr. Romney had hired.

“As far as Mayor Giuliani is concerned, I am a little surprised the mayor says, you know, everybody’s responsible for everybody that they hire,” he said, alluding to the recent indictment of Bernard B. Kerik, whom Mr. Giuliani hired as police commissioner and later in his provate business. “I think we’ve all had people, probably, that we have hired that in retrospect probably it was a bad decision.”

Mr. McCain and Mr. Romney got into a heated dispute on the subject of torture, with Mr. McCain saying that Mr. Romney’s failure to condemn waterboarding reflected a fundamental misunderstanding of American principles.

“How in the world can think that that kind of thing could be inflected by Americans?” Mr. McCain said. Mr. Romney did not back down and also said that he was glad Guantanamo was still open. “I want to make sure these people are kept at Guantanomo,” he said and “not be given legal representation in this country.” Mr. Romney said he opposed torture but would not detail the techniques that are acceptable.Mr. McCain, growing obviously emotional, said, “Then you would have to advocate that we withdraw from the Geneva conventions.”