I would agree that being Obama's boss certainly precludes her at this point, but if she quits, wouldn't all bets be off?
Oh, if she does step down, then it's obvious that she's running. But that doesn't make it any easier for her. As soon as Clinton steps down, everyone will know she's running before she even declares, which may not be a good thing for a prospective Clinton campaign. Besides, it's a terrible risk; why give up SoS to run for president, when you may end up with neither? I'm sure Obama would beat Clinton in a rematch no matter how unpopular Obama is/will be. And if Obama is so unpopular that he
does get primaried, that's not a good thing for Clinton, because she could be tied to Obama too easily.