In any case, I mostly blame Warren. She is the one who chose to escalate to nuclear weapons, saying Bernie said a "Woman couldn't win." Pretty clearly, this is an attack that can hardly go unanswered. If he said it, why is it just coming out now? If he said it, or some version of it, what was the context?
If you decide to bring a gun to what had previously been a pretty civil conversation, you really shouldn't be surprised if you wind up with a bullet hole.