So when and how was it lost? When President Bush’s second-term job approval numbers tanked, despite decent-at-the-time economic numbers, the explanation was easy: It was Iraq, Iraq, Iraq. But nothing quite so pat presents itself in Obama’s case, so here are four partial theories instead.

He gets blamed for Republican intransigence. This is the explanation that many Obama partisans favor, because it lets him mostly off the hook. The theory is that with the country as polarized as it is, and with the public inclined to blame the president for gridlock, the natural state for presidential approval ratings is a kind of regression toward the low 40s. This regression can be interrupted only by either some major unforeseen event or the emergence of a challenger — Romney for Obama, John Kerry for George W. Bush — who reminds voters that they dislike the other party more. But once the challenger is beaten, the process resumes: Just as Bush’s post-9/11 ratings declined steadily except when Kerry was on the scene, so too Obama’s numbers were doomed to decay once he won a second term.

It’s the economy — yes, still: This explanation raises an eyebrow at the last one and says, come on: If the economy were enjoying a 1990s-style boom, surely Obama would have a decent chance at Clinton-level approval ratings, gridlock or no gridlock! But even with the improving employment picture this recovery is still basically a disappointment, especially for the middle class. So the contrast between Obama’s position in 2012 and his weaker one today isn’t necessarily a case study in the economy not mattering. It’s an example of voter patience persisting for a while, and finally running out.