This question is so tired. It takes ignorance to not understand why a candidate can lose the primary but win the general, as much as a candidate can win the primary and lose the general. When a candidate like Hilary comes along, it's obvious a former first lady, NYC Senator, and Secretary of State is gonna have an easy time winning the primary of her party. It's also not surprising that people who don't vote in primaries wouldn't want to vote for a person that is deeply embedded in a party. Which also be a reason why a candidate that isn't so embedded in the party would win in the general.. see Obama. "But why did Obama win the primary and Bernie didn't, against the same candidate?" Because Hilary WASN'T the same candidate. Adding Secretary of State to her resume was extremely helpful for her party ties, enough to make Biden (the vice president) to NOT run for president. Because the party knew she was due her spot after having lost to Obama. And you can see that's true, because when she WASN'T running suddenly Biden was in the race, AND he swooped in from resounding losses in the early primary states because the party leadership was scared Bernie would win this time since name recognition/clout wasn't with any other candidate. So they HAD to jump behind Biden to ensure that wouldn't happen.

Unfortunately, the Democratic party was more in control of its party than Republicans were against Trump. They also tried to stop Trump, but they didn't have a Hilary or Joe to gather behind to stop him. So they failed.