There's a lot of data out there. The majority of his support are young people, like Hoggz, who live and die by Twitter. He doesn't have much support from older people or minorities. Older people are the majorities who vote in general elections. If minorities stay home and don't support the Democratic candidate you saw the end result in 2016. Even though he's running under the "D" he's not a Democrat and lacks support within the party. For example, the largest union in Nevada came out today urging it's members NOT to support Sanders in the upcoming caucus because he wants to do away with their contract negotiated healthcare plans and switch to Medicare for all. Running as a dem and having unions campaigning against you is not a good thing. Also, by most accounts, this capitalism thing has been going ok since the great recession. The economy has grown over the past decade and things are pretty good right now. You can argue whether it's because of Obama or in spite of Trump but jobs are plentiful, 401ks are doing good....I know, let's change it all up and give this Democratic Socialism a try. I don't think that's a winning campaign slogan. In the words of a famous democratic strategist, "It's the economy stupid!!" Also, if this ends up being a contested convention no way are the dems giving him the nomination.
All that being said, he's a good guy. There is a lot I don't agree with him on. But given a choice between him and Trump I'd give Bernie a shot. He'd get my vote.