He's also an unapologetic socialist, which is a very very bad word for huge parts of america. The only reason he beats trump is because trump is such a joke. A real republican candidate would eat him alive - Barring some kind of act of god there's realistically zero chance of sanders being the next president.
An act of god being the not-so-slim possibility of him beating Hilary Clinton? My understanding was that Sanders was giving her a run for her money.
It really doesn't have any Communist connotations to me. Actually, I'm not even sure what being 'socialist' is supposed to mean politically as far as his positions. It's supposed to be to the far left I think, further left than liberal I think.
Edit: Would 'act of God' include Trump going independent and splitting the vote between whoever is the republican nominee? I could see that potentially going for Sanders.
The problem is that these words all mean very different things in modern American politics compared to what they mean everywhere else in the world. "Liberal" in the UK refers to politics orientated around the idea of a small government, pro-economic + civil freedoms, that kind of thing. In America, the word "Socialist" or "Social Democrat" was made toxic by the Cold War and the Red Scare and so on, but the most left-wing "Liberals" in the USA (Sanders, Rage Against the Machine, that kind of grouping) are pretty much Socialists/Social Democrats. The majority seem to be "centre-left" i.e. quite left wing, but in a fairly moderate way - they may disagree with austerity driven politics, they may think that more wealth should be redistributed among the poor, they may think the government should intervene more (and may support larger government). That doesn't necessarily mean they want workers to gain control over the means of production or something. Roughly how far these people think America should go in that direction will decide how "left wing" they are, i.e. how close to the centre.
I should finally add that genuine Social Democrats are "Socialists". You can't be a real Social Democrat without being a Socialist - the whole concept of "Social Democracy" can be reduced to trying to achieve Socialism through gradual reform, using the existing democratic structures, in contrast to a revolution of some kind. In this sense Bernie Sanders is both a Socialist and a Social Democrat. The most confusing thing is that people began using the word "Democratic Socialist", which doesn't necessarily mean the same thing as "Social Democrat" because a Democratic Socialist could theoretically support some kind of armed revolution.