"If we can't get enough other countries to come along with us to do that, then we've got to go with regime change by bolstering opposition groups and the like, because that's the circumstance most likely for an Iranian government to decide that it's safer not to pursue nuclear weapons than to continue to do so. And if all else fails, if the choice is between a nuclear-capable Iran and the use of force, then I think we need to look at the use of force."