If Barack Obama is worried about a conservative backlash against his nuclear disarmament treaty with Russia, the U.S. president isn’t showing it. Obama took a pot-shot at former vice-presidential candidate Sarah Palin after she criticized the deal as leaving the U.S. vulnerable. “I really have no response. Because last I checked, Sarah Palin’s not much of an expert on nuclear issues,” he told ABC News. “If the secretary of defense and the chairman of the Joint Chiefs of Staff are comfortable with it, I’m probably going to take my advice from them, and not from Sarah Palin.” The treaty calls for both the U.S. and Russia to reduce their nuclear stockpiles by a third (to 1,550 warheads each) over the next seven years.