Why would Hillary Clinton suddenly and inexplicably fall on her sword in reference to Benghazi? That question is everywhere today, and for good reason. She is perfectly poised for a presidential run in 2016 whether or not Obama wins his reelection bid this year. And she has earned both experience and respect for her work thus far as Secretary of State. It seems like career suicide for her to take the blame for such an obviously preventable foreign policy nightmare, so why would someone as career driven as Ms. Clinton make such a grievous misstep? There are a few reasons that come to mind.
First: the Clinton name is more or less like political teflon. If Bill's dalliances, cover-ups and half-truths are any indication, Hillary will likely have very few voters even remember any of this in 2016. And those who do remember it will likely believe (as many already do) that she only took responsibility to protect a floundering President. They will see her actions as compassionate, though possibly misguided. And they will love her all the more for the fact that she errs on the side of loyalty.
Second: Barack Obama is facing the first debate of his career that even partially focuses on foreign policy. One of the main criticisms against him in 2008 was the fact that he had little or no foreign policy experience. With four years of continued wars, new wars, and one global snafu or another, we have observed a President who defers instead of leading, who apologizes instead of taking charge, and who bows to people he should be demanding respect from. The Benghazi attack, if allowed to smolder, would become more of a brick wall than a "bump in the road." For that reason, Hillary's move - specifically the timing of her move - is designed to remove at least one weapon from the arsenal Romney could bring to tonight's debate.
Third: Hillary Clinton is likely at least considering her own Presidential bid in 2016. Given that thought, it is unlikely that she will finish out a second term as Secretary of State (assuming that Obama wins reelection). She may be taking this bullet as one final gesture toward the Obama administration before bowing out to pursue her own career track.
Fourth: This will be very easy for her to turn around on the Obama Administration, should she decide to do so in the future. All she has to say is that Obama asked - or even demanded - that she take responsibility, and threatened to throw her under the bus if she didn't. It's easier to recover from the scandal you admit to right away, especially when it turns out to be a setup. Add in the fact that most people already believe that she's taking the blame to throw pressure off the President in the first place...