Ross Douthat writes:

THE 2014 midterms have featured many variables and one constant. Whether they’re running as incumbents or challengers, campaigning in blue or red or purple states, Democratic candidates have all been dragging an anchor: a president from their party whose approval ratings haven’t been north of 45 percent since last October.

The interesting question is why. You may recall that Mitt Romney built his entire 2012 campaign strategy around the assumption that a terrible economy would suffice to deny Barack Obama a second term. Yet throughout 2012, with the unemployment rate still up around 8 percent, Obama’s approval numbers stayed high enough (the mid-to-upper 40s) to ultimately win. Whereas today the unemployment rate has fallen to 6 percent, a number Team Obama would have traded David Axelrod’s right kidney for two years ago, but the White House hasn’t benefited: The public’s confidence is gone, and it doesn’t seem to be coming back.

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. …

It’s the economy — yes, still …

It’s Obamacare — yes, still. …

It’s foreign policy — and competence.