Bernie Sanders supporters would like for people to think that their candidate is the choice of the American people -- and the only reason he is not winning the Democratic nomination is because the system (the rules) are unfair. What they won't admit is that the rules are the same for both Democratic candidate, and neither has been treated unfairly in any way.
The chart above shows the real reason Sanders is losing. It is because millions more voters prefer someone else. In fact, Sanders finishes only third in votes cast this year for president -- behind both Hillary Clinton and Donald Trump. He has gotten 3,167,708 fewer votes than Clinton, and 1,089,289 fewer votes than Trump.
About 21,102,510 Democrats have cast a vote in the Democratic primaries and caucuses. Hillary Clinton has gotten 57.5% of those votes, while Bernie Sanders has gotten only 42.5%. That's a 15 point percentage gap -- and in any election would be considered a blow-out.
Sanders is losing for only one legitimate reason -- more than 3 million more Democrats prefer Clinton to be their nominee.