What interests me here is that there isn't any particular US interest in eradicating the world of Gaddafi, and apart from the bluster of attacking his own people bent on attacking him (a peculiarly internal matter, one might even argue) no new one from a month or so ago.
So given that world leaders pick and choose their rationales like fruit at a Middle East market, we can only judge (I think) the intent by how far today's rationale is from self-interest. As I see it, Obama's failure here is entirely in the realm of domestic politics, which as these things go is exactly the right place you want to weak when lives are at stake.
Which has no bearing on the creation of a new precedent that cannot possibly be consistently adhered to without new conditions to tomorrow's rational for action, or inaction.
[Libya and selective US intervention | Bernd Debusmann | Reuters Analysis & Opinion]