but this simply isn't true.
no one really knew who he was until late 2007, and not really until after Iowa -- where he was a known commodity -- and that's when Hillary's huge national lead, due to her household name status, began to evaporate.
some people knew he gave a spectacular speech in 2004. maybe that he was a Senator. and then maybe that he was a black man running for president.
on a national level, he was not much more than a passing curiosity, a potential star, in the Democratic party. most people probably couldn't have named him or what state he was from. contrast this with our "known commodity" Mrs. Clinton.
i think you're really misunderstanding what is meant by "momentum." you can't have it when you're an unknown. you can only have it when you're a contender, something Obama wasn't, nationally, until *after* Iowa.
what's most true about Obama is the opposite of Mrs. Clinton -- the more people see of him, the more they listen to him, the more they like him.