Barack Obama has a critical choice to make. He can either pursue what one of his aides calls the "tit for tat" negative politics, which the Obama team believes Clinton practices with a vengeance, or he can pursue his themes of conciliation and hope. Obama insiders predict he will stay positive. In addition, Obama advocates say he has developed an important weapon that the punditocracy has been overlooking. Cornell Belcher, a senior adviser and pollster for the Obama campaign, says the many new voters Obama brings into the process would make him a very powerful candidate in the fall. He has the ability, Belcher tells me, to expand and transform the electorate.