Biden sounded almost exasperated as he declared the United States military would leave Afghanistan at the end of 2014.

"We are leaving," he said. "We are leaving in 2014. Period,"

The remarks seemed to rule out keeping U.S. military trainers and advisers beyond 2014, which American generals have quietly lobbied for, fearing the government in Kabul could collapse quickly if it's left to its own devises.

Ryan said his team agrees in principle with the 2014 exit timeline, but called the explicit time frame foolish.

"We don't want to broadcast to the enemy, put a date on the calendar, so they wait us out and then come back," Ryan said.

Biden shot back, arguing that a prolonged presence in a war zone makes the host nation spoiled.

"Unless you set a timeline, Baghdad and Kabul won't step up," the vice president said. "They're happy to let us do the job."