You know, if folks wanted to argue that Presidents really don't have a ton of impact on the economy one way or the other, and thus President Obama doesn't get credit for the recovery, that would be a reasonable point of discussion and there would be at least some truth there in that Presidents often get credit and blame for events that are really more a function of them being in office during a certain time period rather than anything else.
Thus, switch the the script for Reagan and Carter. Reagan is elected in 76, the economy tanks, Carter runs on a program of restoring the economy, wins in 80, and then the economy more or less performs in both cases as it did anyways. Carter gets hailed, Reagan gets panned.
Or flip Bush II and Clinton. Clinton wins in 88 (say he's the VP to Carter). Economy tanks, Bush comes in, wins in 92. Economy roars back, same thing.
Now, Bush II spent a whole lot of money on the wars, Medicare Part D, and tax cuts without paying for any of them. And a lot of changes to how banks work were done by him and Clinton. Those kind of things can't help but affect the economy. But there's a fair argument that most of the time, presidential policies are on the edges.
Or there's even an argument that Obama hasn't done this or that to make the recovery better or faster. I wouldn't agree, but there are reasonable arguments to be made in that vein.
But that's too subtle an argument for some folks. They need not simply for Obama not to get credit, but they need him to be hyper-incompetent, and they need the economy to be "the worst ever" even when there's very little reason to believe that.