A lot of Sanders supporters don't realize how easy Clinton was on him. There was a ton of stuff out there that could have buried Bernie.
If she had treated him the same way she treated Obama in 2008 during the primary, Bernie would be politically irrelevant at the moment.
And on the same hand, a lot of Clinton supporters don't realize how easy Bernie was on Hillary. He took the email issue off the table early on when any other skilled politician would have hammered her on that. I mean, she was under investigation while running and Bernie never went after her on that. There was a ton of stuff that could have buried Hillary (her hawkish foreign policy, fracking, bankruptcy bill that Warren criticized her on). Even though I like Bernie, he's not skilled at getting down in the mud and slinging. Barack attacked Hillary much worse than Bernie did (Board of Wal Mart ring a bell?). She was damaged goods long before Bernie and any sort of arguments in the 2016 primary (which were largely issue focused) pale in comparison to the years worth of damage done on her character by other people. Democrats simply chose the wrong person at the wrong time.