It's too early to completely close the door on Vermont Senator Bernie Sanders' campaign for the Democratic nomination, but there's little doubt that his chances at this point are fairly slender. The Washington Post has an article explaining how Sanders missed his opportunity to win the nomination:
For all that Sanders has achieved — turning a protest movement into a viable run, gaining mainstream acceptance for his democratic socialist views, pioneering a new way to fund campaigns and pushing his adopted Democratic Party to the left on trade, Wall Street and other issues — his campaign for president is also a story of might-have-beens....
According to interviews with the candidate, his advisers, allies and other Democrats, Sanders fell short because of missed opportunities, a failure to connect with key constituencies and stubborn strategy decisions.
Perhaps the campaign’s biggest mistake was not realizing early on that Sanders could win. That led to a slow start, both in building the infrastructure needed to run a national campaign and in Sanders’s own presence among voters who knew little about him.
It's a fascinating read, and one that should be filed away and brought out for candidates looking at the 2020 cycle and beyond.