He won 22 states and has 1870 pledged delegates.
An American political commentator Robert Reich share his point of view concerning a meeting between Clinton and Sanders:
'Bernie’s not a Democrat! Can people not get that through their heads?' said West Virginia Democratic Senator Joe Manchin III, yesterday, frustrated that Bernie hasn’t yet withdrawn from the race. 'I think his mission right now is whatever he can to move the platform further left, from his socialistic ideas. I like Bernie. He identifies the problems, but his solutions don’t work,' said Manchin.
Joe, you’re first point is irrelevant and your second is wrong. Bernie had a right to run in the Democratic primary. And he’s no fringe candidate who must get out before the convention, even though he has little chance of getting the nomination. He won 22 states and has 1870 pledged delegates. Hillary won 28 states and has 2203 pledged delegates.
Bernie's mission isn’t to push the platform 'further left.' The old left-right continuum is beside the point. His mission is to push America forward by loosening the grip of big money on the Democratic Party and on our political system. And his solutions do work. In fact, they're the only way forward.
By staying in, Bernie's not hurting Hillary or helping Trump. He’s keeping as much leverage as possible for as long as possible to achieve this mission – which is the best way to get his supporters (and millions of other Americans) to support Hillary, assuming she becomes the Democratic nominee.