he knows from experience..
Second, a lot of Bernie Sanders supporters werent big fans of Clinton. So Stein campaigning on the idea that Clinton and Trump were similar made it harder for Clinton to win over those voters even if Sanders voters didnt vote for Stein, they may have stayed home out of disgust.
https://fivethirtyeight.com/features/jill-stein-democratic-spoiler-or-scapegoat/
"The Liberal Case Against Bernie"
Senator Bernie Sanderss presidential candidacy poses a conundrum for progressives. Not since 1936, when Franklin Roosevelt said that he welcomed the hatred of corporate interests, has a serious presidential candidate offered so aggressive a challenge to the conservative powers that be. At the same time, however, a dangerous lunatic is president of the United States, and Sanders, of all the major Democratic contenders, is the one who will make Donald Trumps reelection most likely. Eight years of a Trump presidency could mean the end of meaningful democracy in the United States, along with many of the rights that women, minorities, immigrants, LGBTQ people, and others now take for granted.
Let me clarify: Ive been a fan and supporter of Sanders ever since he was elected mayor of Burlington, Vermont, in 1981. I was honored to be asked to testify before him in Congress years ago, and I voted for him in the New York presidential primary in 2016. I did so, however, not because I imagined he might win the nomination, but because I hoped that a strong showing by Sanders would help wake up Hillary Clinton to the importance of addressing economic inequality, and also to honor his brave criticism of Israels occupation of the West Bank.
I was wrong. Sanders turned so negative toward Clinton that it hurt her in the general election. Even though he campaigned for her after he lost the nomination, roughly 12 percent of Sanderss supporters switched to Trump, and enough of the rest supported Jill Steins kamikaze candidacy that it helped tip key states to Trump.
I see he's into reality.
https://www.thenation.com/article/bernie-sanders-electability-eric-alterman/
https://www.democraticunderground.com/?com=view_post&forum=1287&pid=42334