In Debate, Romney and Giuliani Clash on Immigration Issues

McCain, whose campaign was damaged by his support for comprehensive immigration legislation, promised along with others that, as president, he would secure the borders, but he called on his rivals to tone down their rhetoric on the hot-button issue. If he becomes president, he said, "We won't have all this other rhetoric that unfortunately contributes nothing to the national dialogue."

Tancredo, the most outspoken opponent of illegal immigration in the Republican field, stood quietly through most of the early minutes. "All I've heard is people trying to out-Tancredo Tancredo," he said.

There were moments of levity, often provided by Huckabee, whose best line of the night was in answer to a question about what Jesus would do about the death penalty.

"Jesus was too smart to ever run for public office," Huckabee said, prompting laughter on the stage and in the audience.

But the debate repeatedly turned serious and confrontational. One of the toughest exchanges came over torture, pitting McCain, a prisoner of war in Vietnam, and Romney.

A questioner asked whether any of the candidates disagreed with McCain's contention that the practice of waterboarding constitutes torture. Romney, asked to answer first, hedged, saying that as a candidate for president, he would not specify which techniques he considers torture.

McCain could barely conceal his contempt, saying he was "astonished" that Romney would think the practice might not be torture. When Romney persisted that he would not talk specifics on the issue, McCain ripped him a second time, saying that would mean "you would have to advocate that we withdraw from the Geneva Conventions."

Arguing that this is a defining issue for the country, McCain concluded by saying, "We should be able, if we want to be commander in chief of the U.S. Armed Forces, to take a definite and positive position on, and that is, we will never allow torture to take place in the United States of America.

Later, McCain and Paul clashed over Iraq and foreign policy, with McCain accusing the congressman of the kind of isolationism that allowed Adolf Hitler to come to power in the 1930s.

Giuliani got a question about a report Wednesday on Politico.com about security expenses for mayoral trips to the Hamptons that were allocated to a number of obscure city agencies.

Giuliani denied any wrongdoing, saying New York mayors are provided round-the-clock security. He said he knew nothing about the expensing: "They were handled, as far as I know, perfectly appropriately."

Democrats participated in a YouTube debate in July, but a number of GOP candidates balked at joining a similar forum scheduled for September. They criticized the Democratic debate as undignified, deriding one question presented by a snowman.