Barack Obama has opened up his widest national lead over Hillary Clinton since late March, running ahead of her by 51 percent to 41 percent, according to the Gallup daily tracking poll conducted April 6-8. The margin of error is 3 points. The last time Clinton led Obama by any amount was in Gallup’s March 18-20 survey. Not much new to report on general election match-ups with McCain. None of the candidates hold a statistically significant advantage there.