Read this piece from a Daily Kos user about his journey from Bernie to Hillary. I don't share this journey - I've been for Hillary from the start - but the piece details a lot of the reasons why I can't support Bernie Sanders. Another important set of works are the Looking for Bernie series at Shakesville (mentioned in this Kos piece), which convincingly puts to death the notion that Sanders is not a traditional politician.
(Long aside, and maybe this should be its own post, I think traditional politicians are good, I think they're what's needed to solve political problems. I just have a problem with someone who's been in the U.S. House and the U.S. Senate for the past 27 years trying to claim they aren't a traditional politician.
A simple look at his voting record shows he's not a brave loner, bucking the wishes of his constituents. All of his 'bold' votes are right in line with what his constituents wanted him to do. It's not bravery to vote the way your constituents want you to vote. It would have been brave for him to voted for the various pieces of gun control legislation he's opposed; that would have been going against his constituents wishes. But as he's said on many occasions, he didn't vote for those measures because it would have cost him votes to do so. But I digress.)
Neither set of works gets at the biggest problem I have with Sanders, though.