He said he was sick and tired of hearing about the emails. He didn't say the FBI/DOJ investigation should end.
I just wish politicians of all stripes would get it in their heads that the proper response to a question about anything related to an ongoing investigation is "I'm sorry, but due to the fact that there's an ongoing investigation on that subject, I won't comment at this time." Simple, right? But democrats can't seem to do it, republicans can't seem to do it, heck, the sitting president can't seem to do it. My objection is not to the change in Mr. Sanders' response, my objection is that he (and many others) feel the need to play politics with what I believe to be a very serious matter: those damn emails.
That's the right response for someone who is involved in the investigation which Sanders is not. All he did was the minor step of correcting the misunderstanding that he opposes an investigation.
Going after her constant flip-flops is the bigger thing and stems from the entire reason Sanders is running. Remember this is a guy who is in his 70s, never run for president before, tried to pressure Obama from the left during his presidency, and didn't get in this time until Warren insisted repeatedly she wasn't running. Which is to say, unlike almost every other candidate for president, Sanders appears to be driven by issues not personal ambition. His forum appearance was telling. He laid off Hillary almost entirely and in answer to his dream non-politician job said president of CNN, which wasn't about fun but affecting the national conversation. Sanders doesn't really expect to win the nomination but he wants to move Hillary to her left and pressure her to stay there.
She might end up being a better president thanks to American hero, Bernie Sanders.