Democratic White House hopeful Barack Obama has surged to a 15-point lead over Republican John McCain in the latest US poll out Friday, by far the biggest margin of any recent survey. A US magazine's poll gave Obama 51 percent to 36 percent for McCain among registered voters nationwide three times the margin of four to five points that other polls this week have given the Illinois senator. Obama is enjoying a post-primary bounce after seeing off the dogged challenge of his Democratic rival Hillary Clinton earlier this month, and supporters of the former first lady are flocking to his side, Newsweek said.