She doesn't have the political skill or charm of either Obama or her husband so will get nothing done.
This is a big aspect of politics that so many people fail to understand. The overwhelmingly common view of politics is some kind of mathematical equation whereby accomplishment is determined solely by the placement of people on a 1 dimensional left right spectrum. This view is not only childishly simple, but voting based on this view is actually harmful.
The general population of reddit prides themselves on being very analytical and logic based. And I don't mean to suggest that acting predominantly on logic is inherently bad. I myself tend to act more according to logic than emotion. But good effective application of logic also requires accurate understandings of how things work, and when it comes to politics those of us who are logical must incorporate an understanding that many (most?) people engaged in politics aren't.
Let's take a minute and go all the way back to Aristotle. He described three methods of persuasion: Logos (logical consideration), Pathos (emotional reactions), and Ethos (Belief in a person's integrity/trustworthiness, or credibility.)
Now to apply these to politics, I think it should be noted that many people, including politicians, adopt their initial views according to pathos, and then try and justify/support them with logos. This is true for both republicans and democrats. Take immigration: Many (not all) people who are anti immigration are primarily motivated by fear: fear of the terrorists or of violent cartels, or whatever. They then try to rationalize these fears and come up with statistics that support or reaffirm them. Similarly democrats are often motivated by compassion, by the sense that there are disadvantaged people in the world that need our help, and that it is our duty to provide it. They also find facts which reaffirm these emotional beliefs. (I should not that the further I get into academia, the more I realize that there are facts to support anything you want. I love academia, and I love the process of research and debate about results, but....putting too much stock in any given paper by some dude who was smart and said some smart things that he supported with data is inadvisable....because almost always there's another smart person with criticisms also supported by different data. The deeper I get into my pursuit of knowledge, the more I discover how unattainable knowledge is....which is a Reddit rant for another time.)
But in terms of the actual act of governing, Ethos is just as, if not in many ways the most, important. Policies aren't determined nearly as much by the ultimate balance resulting from the collective placement of our elected officials on a conservative-liberal dichotomy. It matters much more how the people on different ends of that scale feel about people on the other. "Polarization" isn't so much the result of people moving away from the middle and towards the ends of this scale. That's more of a symptom than a cause. Polarization is caused by a an absence of Ethos among those we elect. Distrust and general dislike. Republicans in congress didn't obstruct Obama because he was "and extreme leftist". He wasn't! They obstructed him because they didn't like him, and because their constituents didn't like him, either because of race or just because of his seeming like an highbrow city liberal who couldn't relate to the working man.
People like to say that we shouldn't vote for a president based on personality, but I think we absolutely should! Presidents who are relatable and personable, who have a high degree of Ethos....they are more effective. They can be on any end of the left-right spectrum, but if they evoke feelings of trust and reasonableness, then they will be more effective.
I've heard 100 times in this election cycle from Hillary supporters that she will be able to get more done than Bernie because she's more centrist and he's more extreme. But that's just not the way politics works. She's more centrist and can might be able to make more logos based appeals....but her pathos quality is not just weak....it's negative. She doesn't evoke trust, she evokes distrust. She isn't liked, she is hated. And it's easy for her supporters to say that it isn't fair or it's just based on misunderstandings or whatever. I think it is in fact her own fault but the hard truth is that it doesn't matter. Because pathos isn't based on logos. It's based on a perception and whether or not the perception is "fair" or not is irrelevant to the goal: effective governing. Clinton will be the most polarizing president we've ever had, in my opinion. She won't be able to get anything done, no one will want to negotiate with her centrist views, she won't be able to "get things done" because she lacks any degree of pathos persuasion.
Sanders, despite being possibly the farthest left candidate since FDR, has what Hillary doesn't, the perception of integrity. He may be vastly ideologically different than republicans, but he is respected. They may think his positions are extreme, but I don't think a single republican believes that he is corrupt, that he isn't doing what he genuinely thinks is best. And so they will work with him because of his pathos appeal.
I've said this before: Presidential Elections will always be, at least in part, popularity contests. That doesn't mean it should be the only factor we consider, but likability of a candidate shouldn't be dismissed as irrelevant either. Because perceptions of likability matter, and directly effect the likelihood of accomplishment and results within the actual act of governing.
TL:DR My mom had a cocaine fueled threesome with Obama and Michelle back in the late 80's.