In its most recent poll, Gallup found that the President Obama's approval rating on the economy has dropped to 35 percent — down seven points from June. It's not his lowest rating ever, but it's in the lower ranks.

But why? What's the motivator for peoples' changing opinion of Obama's performance, particularly given the president's new focus on the issue? We looked at four different economic indicators to see if any correlated to the fluctuations of opinion over time.

The short answer is that none is a clean fit. Which isn't a big surprise: Gallup's polling is as precise an instrument as possible, but it has a margin of error, like any poll. And perceptions of the economy are almost certainly a function of a confluence of things, including the elements below. (For the purposes of comparison, we isolated only the first indicator of the months for which Gallup polling exists.)

Regardless, there was at least one indicator that comes close. Here are the four metrics. Click the links beneath each graph to change the comparison.

Approval on the economy (Gallup)

Change to:

Do you see the one that's the closest fit? Perhaps this makes it more clear. In the graph below, we compared each data point to February 2009 as a baseline.

As Gallup itself noticed in 2012, its economic confidence measure links to Obama's approval rating — overall, not just on the economy, but the correlation fits loosely here.

Gallup isn't alone in noting that relationship. Last May, Nate Silver noted the link between Obama's approval on the economy and his overall approval. If people feel more confident in the economy, they feel more confident in the president that's running it. Since June, that first indicator of confidence has dropped.