John Edwards has leapfrogged over his rivals Hillary Clinton and Barack Obama, and leads the Democratic field in Iowa, according to the latest InsiderAdvantage/Majority Opinion poll. The race among the three top Democrats is extremely close, with the potential for any of them to finish first – or third. Edwards leads with 30 percent in a poll of Democratic voters who said they intend to participate in the Jan. 3 presidential caucuses, followed by Clinton with 26 percent and Obama with 24 percent. When the sample was narrowed to the most likely caucus-goers, based on several questions, Obama leads Edwards...