One of the most-oft used attacks against Bernie Sanders by corporate Democrats is that he should be rejected because he, "isn't even a Democrat!" These attacks on Sanders are made by these DNC devotees without irony. To them, and people like them, unquestioned devotion to your "team" is far more important than logic, morality or ideology. For these mindless collectivists, adherence to orthodoxy and unquestioning subservience are the most laudable attributes. The Clinton dead-enders blame Bernie for Trump's victory, instead of realizing that most American people despise Hillary Clinton and everything she stands for.
What these corporate stooges and ignorant Clinton devotees cannot understand that a large part of Bernie's appeal is that he isn't part of the Democratic party. The party of Hillary Clinton, Nancy Pelosi, Harry Reed and a bunch of other 80 year-old corrupt, police-state supporting warmongers is not appealing. Unfortunately, the Clinton wing of the Democratic party (who still holds the reigns of power) would rather keep collecting checks from their Wall Street masters and lose elections than support fair, rational policies and miss out on their payola.