Fresh polls show that he has been unable to convert weeks of extensive media coverage into a widened lead. And some prominent Democrats whose support could boost his campaign are still not enthusiastic about his candidacy. Several new surveys show that Obama is in a tight race or even losing ground to Republican John McCain, both nationally and in two important swing states, Colorado and Minnesota. One new poll offered a possible explanation for his troubles: A minority of voters see Obama as a familiar figure with whom they can identify. Many voters still seem to be puzzling over who...