Updated

John McCain, a Vietnam war prisoner, argued Friday that his top rivals for the GOP nomination aren't qualified to deal with issues like torture -- or to be president in wartime -- because they never served in the military.

The Arizona senator's position on an interrogation technique that simulates drowning -- he says it constitutes torture and is illegal -- puts him at odds with Rudy Giuliani, Mitt Romney and Fred Thompson, who haven't taken such a hard line.

"There's a clear division between those who have a military background and experience in these issues and people like Giuliani, Romney and Thompson who don't -- who chose to do other things when this nation was fighting its wars," McCain told reporters after touring a shipyard and taking questions from workers wearing hard hats and blue jeans.

He stepped up his criticism of his opponents in the midst of a three-day visit to an early voting state with a heavy military population and as a new Winthrop University/ETV poll in South Carolina shows him in single digits and trailing the trio.

In Iowa, Romney said that while he respected McCain's service in Vietnam and in the Senate, his own service in the private, public and non-profit sectors was "highly relevant to lead the nation at a time where we face such extraordinary challenges."

Aides for Giuliani and Thompson dismissed the criticism.

McCain questioned his rivals on their lack of military service even though he suggested during the 2004 election that military experience shouldn't be an issue.

Standing in a shipyard warehouse Friday, he focused on comments Giuliani made a day earlier on CNBC. The former New York mayor said "waterboarding" should not be used in every circumstance, but he also left the door open to it.

"I'm very reluctant to take away presidential prerogatives and decision making, maybe because I've faced crisis more than the other ones have," said Giuliani, who was praised by many for his performance in the aftermath of the Sept. 11, 2001, terrorist attacks.

McCain, a former Naval aviator who was tortured in his 5 1/2 years in a North Vietnamese prison, responded: "Mayor Giuliani just contradicted himself because anybody who has experience in warfare knows that waterboarding is by any definition torture and cannot be condoned. I do not know which crisis the mayor may have been talking about. My experience goes back to the Cuban missile crisis and every conflict we've been in since."

Then, McCain broadened his broadside to also castigate Romney, the former Massachusetts governor, and Thompson, the former Tennessee senator, as well as Giuliani on Iraq. He argued they were "nowhere to be seen when we were fighting a war with the wrong strategy."

"I never saw Romney, Giuliani or Thompson say a word about it, except supporting what I clearly pointed out was a failed strategy," McCain added. He said he has called for more troops in Iraq since 2003 and saw President Bush embrace that proposal earlier this year.

"I don't think there's any greater indication of experience and knowledge of how wars should be fought and how crisis should be handled."

Giuliani's spokeswoman, Maria Comella, said her boss has clearly stated that "if we're going to defeat the terrorists then we must use aggressive questioning. And in those extraordinary circumstances, the president needs all options available to ensure the safety and security of Americans."

Said Thompson spokeswoman, Karen Hanretty: "We all respect Senator McCain's military service, however, there are many great Americans who have served this country and not worn its uniform."

None of the three enlisted. Draft deferments kept Giuliani out of Vietnam while he attended law school and worked for a federal judge; he had twice been eligible for the draft. Romney received a draft deferment while serving as a missionary in France during the war. He was eligible for the draft later, but was not selected. Thompson, with a wife and child, was deferred from service.

McCain assailed his rivals on torture even as he defended his decision to vote for Michael Mukasey's nomination to be attorney general despite being troubled by the nominee's initial answers about waterboarding. McCain said he was confident that Mukasey would not allow the method because of his answers to written questions.