Was it an eleventh-hour tide of sympathetic women, people reluctant to say they were not backing a black candidate or problems with the polls themselves? For whatever reason, late public opinion surveys showed Barack Obama cruising to a triumph in the New Hampshire Democratic primary. Pollsters and other analysts floated all kinds of theories on Wednesday, a day after Hillary Rodham Clinton salvaged her candidacy with a startling 39 percent to 36 percent victory over Obama. Muddling the hand-wringing, most of those same polling organizations, using the same techniques, forecast John McCain's 5-percentage point win with admirable accuracy. "I don't think anybody knows for sure the problem at this point," said Mark Mellman, a Democratic pollster who is not working for a presidential candidate. Polling of Democrats just before Tuesday's vote gave little warning of the New York senator's comeback, with most underestimating her strength. A USA Today-Gallup Poll gave Obama a 13-percentage point lead, putting her at just 28 percent. Another by CNN, local television station WMUR and the University of New Hampshire had the Illinois senator up 39 percent to 30 percent.