A federal appellate judge expressed deep skepticism Monday about a Justice Department lawsuit challenging Arizona's new immigration law, leaving uncertain the Obama administration's chances of stopping the law from taking effect. "I've read your brief, I've read the District Court opinion, I've heard your interchange with my two colleagues, and I don't understand your argument," Noonan told deputy solicitor general Edwin S. Kneedler. "We are dependent as a court on counsel being responsive. . . . You keep saying the problem is that a state officer is told to do something. That's not a matter of preemption. . . ....