John McCain has a slight lead over Barack Obama in the latest Gallup daily tracking poll conducted March 11-15, leading him 47 percent to 44 percent, while remaining tied with Hillary Clinton at 46 percent each. The margin of error is 2 percent. In the Democratic nomination contest, Obama leads Clinton 48 percent to 45 percent, with a 3 point margin of error. That survey was conducted March 13-15.