Since the start of these races, the campaign party of Bernie Sanders has always attacked and vilified Hillary Clinton's actions and representations. Of course it will continue like this unabated until one of them wins or the other backs down because of too much bad publicity. I believe it is part of the political game.
It is clear that Bernie Sanders gave criticisms of Hillary and her policies as early as November of 2015, and only recently has the media been following all the attacks that Hillary has given in return. It was widely talked about that his strategy was to separate himself from the policies and tactics of Clinton. On order to do that, he had to eventually start to distinguish himself from her.
Hillary is great at acting like she's allowed to insult people and nobody is allowed to scrutinize her past, or even talk bad about her. She even told her secretary (the one who runs her Facebook page), to delete any comments that say anything bad about her. When it comes to insults, Hillary has a double standard. She's been badmouthing people long before they've insulted her, and she always cries feminism when they retaliate.
On the Democratic side, the dialog between the candidates has been civil and progressive. "Attacks" by the candidates come mostly in minor criticisms or fundamental disagreements how they approach an issue, (for example, gun control). From what I can see, the democratic discourse has mostly been based on building a brand, something for the long-term as an opposition to the reactionary, hyperbolic republican in-fighting.