Bernie Sanders is representing the young, the poor, and the downtrodden. Unfortunately, thanks to the "Great Recession" there are more of these people than there are those who have wealth and prestige. Depending on how many people any of the corporate sponsored candidates can fool into thinking they are the poor man's candidate, Sanders has a really good chance of beating the rest in a race to the white house.
People are tired of this country being bought out by billionaires. Bernie Sanders is that beacon of hope and has the potential to start a political revolution. With the majority of the population living in poverty, over-crowded prisons, and outrageous student loans, there's no argument that they will turn to Bernie.
Bernie Sanders is widely popular with the younger crowd, but these tend to be the people that don't get out and vote, especially in the caucuses. I think that, although he has many supporters, he won't make as good of a show as people anticipate on caucus night. He might remain close, but in the end I think he will lose to Hillary Clinton.
No, even though Bernie Sanders' has a popular following among his constituents and through social media, public popularity is not enough to win a presidential nomination. Many of the people who loudly support his candidacy do so for the sake of appearances and personal ideologies, but are not motivated enough to actually show up and vote in the primaries. We saw this in the past when George W. Bush won a second candidacy despite widespread disapproval in popular media, due in part to low voter turnout.