Obama pledges anew to "stand with Israel" if it is attacked by Iran, but ducks the direct question of whether he considers an attack on Israel to be the same as an attack on the United States. Romney also says "we have their back" if Israel is attacked.

Both state their complete opposition to allowing Iran to develop nuclear weapons but do not define their "red lines" across which Iran must not cross.

Romney gives some new options for countering Iran's disputed nuclear program, including indicting Iranian President Mahmoud Ahmadinejad for war crimes and says Obama should have done more sooner to hit Iran with sanctions.

Obama directly denies a published report that his administration has agreed in principle to direct bargaining with the Iranians but defends diplomacy as the best option now.

"The clock is ticking" and the United States won't let Iran bargain endlessly without result, Obama says.

Some of Romney's toughest language of the night on Obama as too quick to negotiate with despots, and a repeat of the claim that Obama took an "apology tour" around the world early in his term. Obama calls that a "whopper."