Originally Posted by The Great Zaganza
Yes, it may sound appealing to be the "outsider" who can get in there and mess up the status quo. But there are problems with that.
It means Sanders will be limiting allies that he can call on during the primaries. (If you're a life-long democrat who has spent years trying to build up the party, you will be less eager to support the guy who swoops in at the last minute to say "I'm taking over now".) Fewer endorsements, fewer voters willing to give you a chance.
It also means that during the election itself, some voters and campaign workers will be less enthused at the "outsider" who has come in at the last minute. "Support me as a candidate... even though I think you democrats were bad people".