A new Rasmussen poll is turning some pundits' and bloggers' brains to mush.

Voters Perceive Obama Moving to the Middle

During the Primary campaign season, Obama was viewed as politically liberal by an ever-increasing number of voters that grew to 67% by early June. However, since clinching the nomination, he has reversed that trend and is now seen as liberal by only 56%.

So what caused that shift? Was it Obama's allegedly center-moving shifts on FISA, Iraq, guns, and God? Let's look at the calendar.

The shift for Obama is clear through the weekly surveys taken in June. Twenty-nine percent (29%) of voters surveyed June 7-8 rated Obama Very Liberal; by June 28-29, that number had fallen 5 percentage points to 22%.

First, the math doesn't add up - 29-22=7%, not 5%. But either way, that's a relatively small decline.

Second, the dates don't add up. Most of Obama's alleged "shifts" were during the week that ended June 28-29. But they were each small stories that got little or no coverage during that week. The broader narrative about Obama "moving to the center" didn't emerge until over the July 4th holiday and is therefore not the most likely cause of the drop, however small it is.

If the drop in liberal perception was statistically significant, it's more likely due to other causes - perhaps a comparision with the ever-more-conservative John McCain, or perhaps just a growing familiarity with and approval of Obama.