GOP contenders argue on Afghanistan, Iran, torture

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 remarks 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 as commander in chief of the military.

Huntsman, who served as Obama's first ambassador to China, said it was time to withdraw all U.S. troops from Afghanistan.

"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 about when to withdraw troops.

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.