You can say what you want about socialist Bernie Sanders, on this he is not wrong:
Sanders (I-Vt.) never mentioned the former secretary of state and current front-runner for the Democratic presidential nomination by name, but his message was clear: He has been a man of conviction, prepared to upend the system; she is too often a political weather vane, too cautious and catering to the political establishment.
That is not to say that Hillary doesn't hold some very progressive convictions. She's just more sneaky about them - not willing to come across as progressive for fear of losing supporters, unless she's talking to a progressive audience. Indeed she's not afraid to abandon those convictions in favor of winning - sometimes even contradicting herself within the same debate.
Still, the Washinton Post was quick to come to Hillary's defense in the same article, opening with this:
Bernie Sanders has long said that he would not run a negative campaign against Hillary Rodham Clinton. But his campaign took on a decidedly sharper edge Saturday night at the Iowa Democratic Party’s Jefferson-Jackson Dinner.
It will be interesting to see, with Biden not hopping into the fray, whether Sanders feels he has to step up his negative game going forward.