The more rabidly left-wing Democrats distrusted Bill Clinton when he first ran because of his connection with the Democratic Leadership Council, which was a mechanism to fool people into thinking he was more moderate than other Democratic contenders. That, plus being a native of the South.
So even though Hillary is probably more of a leftist than Bill, there are probably a lot of Democrats who want someone more trustworthy, a Northern leftist with no taint of "moderate" about them.
Well, Mitt Romney is available...