Sanders has the majority support of young democratic voters. Young voters are often the ones who are unaccounted for...who do not show up to the poles. BUT, with passion for what Sanders stands for, they may show up this year to win the vote. In addition, Clinton continues to fail at gaining back the trust of many Americans.
It is my belief that the candidate is surging ahead in the polls. His stand on issues and outgoing personality is gaining following with a large voting demographic, the millenials. The voting pool is increasing with younger voters whose ideas about government and how the presidency should be obtained and held is very different from 20 years ago. He is appealing to this young voting pool and is doing do successfully.
It is difficult to tell by polls sometimes, but if Hilary Clinton was the presumed candidate from the start, that promise is waning. It does not seem that she is the presumptive candidate any longer. Bernie Sanders seems to speak to the people in a way she cannot. I am not American, but this is just what I've been reading.
Hillary Clinton has been the assumed candidate for months, and while Senator Bernie Sanders appears to be surging in some polls, it is not the case that he will be able to maintain his momentum through March. Bernie came to a virtual tie in Iowa, and dominated Hillary Clinton in New Hampshire, but his margins of victory were not wide enough to carry him into territory that has been dominated by Hillary for months. She has the organization, her support lies more firmly in people who historically go out to vote (ie. not young people), and she is leading in all national polls. Bernie won't sustain the momentum. He needed to win by more in Iowa and New Hampshire to compete.