I understand that Sanders is basically saying that Clinton has no strong philosophical core, but, out of blind ambition, says whatever she thinks will appeal to the demographic crowd she's addressing at any given time.
That's a political judgment about which people have their opinions. With rare exceptions, I don't express political preferences here.
But I do object to the notion that a person can't be a moderate progressive. Or a moderate conservative or a moderate liberal.
To me, being a moderate defines how one approaches political issues, not a specific set of political propositions. As I wrote in a piece for The Moderate Voice nine years ago:
Frankly, I'd like to see a lot more moderation in our politics, whatever the politicians' party or philosophy. I said back then:
For our politics to work in this deeply Red-and-Blue-divided nation, we need a strong dose of the moderation our Founders enshrined in our Constitution. Around the world today, we’re seeing that it isn’t enough to grant people the vote. Immoderate voters elect immoderate leaders, people who are duly-elected despots, tyrants, and hare-brains.Moderate voters and moderate candidates, whatever their political philosophy, form better governments.