I love Bernie. I'm probably voting for him in the primaries, mostly because California's primary is so late it doesn't really matter.
That being said, I do get a little annoyed by those on the left at how poor they are at engaging within the political process except to vote for president once every four years. At this point, there are only a few politicians in the Senate I'd consider true "progressives": Bernie Sanders, Elizabeth Warren, Sherrod Brown, Amy Klobuchar, Al Franken, Jeff Merkley, and Tammy Baldwin (I'm admittedly less familiar with members of the Hawaii delegation, along with a few other states). There's only 68 voting members of the Progressive Caucus in the House.
So even if Bernie is elected (and let's just assume his successor in Vermont is also a progressive, probably Peter Welch), what can he do? By not engaging in the primary process in not just 2016, but 2014, 2012, 2010, 2008 etc, you're setting yourself up to fail. Populist politics can work in swing states and swing districts -- see Sherrod Brown, Ann McLane Kuster, Rick Nolan, Peter DeFazio. People not getting involved in the process early enough are the real cancer, especially those who then go on to decry their choices by saying "it's all the same, man." At least understand the choices and the context with the choices as well as the state/district/country's demographics that you're working with are paramount when understanding who to vote for!
Also -- Vermont is one of the whitest states in the country. That just isn't the Democratic party's demographic. Until he can figure out a way to appeal beyond white, liberal enclaves like Madison and Denver, his appeal only can go so far.