Kevin Drum notices an interesting correlation in the gyrations of the Gallup poll of the House ballot:

It turns out that the Democratic surge is largely due to a sudden jump in support from independents. So what caused that? Well, I was struck by an unusual correspondence between two of Gallup's charts. It turns out that whenever enthusiasm goes up among registered Republicans, preference for Republicans goes down among independents. The pasted-together chart below — it's a little messy I'm afraid — shows five cases of a jump in Republican enthusiasm (top chart) along with the corresponding drop in Republican support among independents (bottom chart). It's not a perfect correlation, but it's a pretty good one.
Anyway. Here's my guess: every time Republicans do something that gets the tea party base excited, it simultaneously turns off independents. I'm not quite sure what caused the latest jump (NBPP fever? tax cuts pay for themselves? unemployment compensation obstructionism?), but apparently it was something.

I suspect this is a coincidence, but it's interesting enough to keep an eye on.