GOP contenders argue on Afghanistan, Iran, torture

Paul wanted no part of a military strike. "It's not worthwhile to go to war," he said. He added said that if America's security is threatened the president must ask Congress for a formal declaration of war before taking military action.

Perry responded without answering the question. "This country can sanction the Iranian central bank right now and shut down that country's economy, and that's what the president needs to do," he said.

The United States has long had sanctions in place against Iran, and Obama's news conference in Hawaii suggested there will soon be more.

The war in Afghanistan produced the same range of responses as the question relating to Iran's nuclear ambitions — unanimous criticism of the president but differences among the Republicans seeking to take his place.

Huntsman, who served as Obama's first ambassador to China, said it was time to withdraw all U.S. troops from Afghanistan, a land where their boots first touched the soil a decade ago. "I say it's time to come home. I say this nation has achieved its key objectives," he said.

Romney and Perry said they would side with military commanders on the ground about when to withdraw troops. They criticized Obama for "telegraphing" the nation's intentions.

Yet Romney backed a timetable of a complete withdrawal by the end of 2014, the same that Obama has cited.

Obama's would-be successors differed on waterboarding, as well, the interrogation technique that former President George W. Bush authorized and Obama has banned.

While Cain and Bachmann both said they would reinstate the technique, Huntsman said use of the procedure diminishes U.S. standing in the world and Paul said it is illegal.

Romney wasn't asked directly, but said he would "use whatever means necessary to protect America."

Perry said, "This is war. That's what happens in war. I'm for using the techniques, not torture, but using those techniques that we know will extract the information to save young Americans' lives — and will be for it until I die."