I think Matt overestimates the relevance of actual policy positions to the success of political candidates in this post on Hillary Clinton. Indeed, while it's fairly clear that Americans aren't terribly familiar with the nuances and straddles in her substantive views, it isn't clear to me which of those views would actually prove unpopular. She's notably unapologetic about her support for the Iraq War, for instance, but she's not actually outside the mainstream in her promise to end it if she becomes president. And her larger foreign policy perspective, which remains somewhat more militaristic and impressed with American power than either Matt or I are comfortable with, is probably closer to that of the median voter than a more progressive stance. It's just not clear to me, in the end, which policy position, if widely understood, would actually doom her candidacy.
And all that aside, if you're evaluating public appeal, I think it's generally a mistake to spend excessive amounts of time gaming out how various policy positions map out onto the median voter's ideological matrix. The median voter, as many studies in political psychology have shown, rarely tends to have an ideological matrix, and judges candidates in a more intuitive, do-I-like-them-or-not sort of way. Hillary is actually pretty likable, and will have little trouble attracting broad support.
Now, I think Hillary isn't terribly progressive, and so the question is partially how to make that point to Democratic primary voters, which is the group who'll hopefully find that particular argument compelling. But I don't think it's a surprise she's a common second choice, and I don't think affection for her rests on on too many misapprehensions about her record. Even Democratic primary voters are significantly less liberal -- or at least dogmatically liberal -- than I would prefer them to be. And even of those that in my ideological neck o' the woods, opinions often aren't formed on ideological questions so much as gut level intuitions. Meanwhile, she;s currently playing the role of generic Democrat, and so when low-information voters lose their first choice, it'd be more of as surprise, at this point, if they didn't go to her.