NEW ORLEANS (AP) - President Barack Obama and Republican Sarah Palin sparred from a distance over nuclear policy with each questioning the other's experience on the issue in a potential preview of the 2012 White House race. "Unbelievable," Palin said earlier this week after Obama rewrote the U.S. nuclear strategy, and she suggested the president was weak on nuclear defense. Obama, in Prague to sign a nuclear reduction treaty with Russia, countered by deriding the former Alaska governor who resigned midway through her first term as "not much of an expert" on nuclear issues.