So, naturally, the Democratic Party establishment is doing everything they can to sideline him...
He's not a Democrat. He changed his party affiliation days after the DNC convention (that's how toxic he regards the Democrat party). If Bernie actually wanted to transform the party, he'd have to actually be in the party. Bernie wants have it both ways. He cannot.
And, how is Hillary adopting a large part of his agenda "sidelining" him?
And, the Democrats tried Bernie 40 years ago when he was called George McGovern. Bernie is the Democrat's Ted Cruz: he has hardcore support, but not broad appeal. For some reason Bernie supporters cannot get it through their heads the same way Cruz supporters cannot.