[Update (6/30/10): Serious questions have been raised about the validity of Research 2000's polls. The results discussed below should thus be viewed as potentially suspect until the matter is resolved.]
Two new polls are out measuring the state-level prevalence of the misperception that President Obama is not a citizen of this country.
Tom Jensen of Public Policy Polling has released a preview of a poll showing that 47% of North Carolina Republicans think President Obama is not a citizen -- an even more disturbing finding than his previous poll, which found that 41% of Virginia Republicans believed in the myth. By contrast, a Deseret News/KSL-TV poll found that only 13% of Utah Republicans -- and 9% of Utahns generally -- said that they believe Obama is not a citizen (via David Weigel).
These results are consistent with the national figures from a Daily Kos/Research 2000 poll, which found that the myth was endorsed by 28% of Republicans (and 11% of Americans) overall and that it was more prevalent in the South.
What explains the state-level differences in birther misperceptions that we observe? The Washington Independent's David Weigel suggests the difference may be linked to a lack of racial polarization in Utah:
So why does rock-solid Republican Utah have fewer “birthers” than, the deep South, or even fewer than blue Virginia and North Carolina? A lack of racial polarization has something to do with it. Utah, like the rest of the great plains and western states, got bluer in 2008 despite overall McCain victories and despite having a very, very white population. In Utah, Obama got 327,670 votes in 2008, up from the 241,199 votes that Sen. John Kerry (D-Mass.) got in 2004. For the first time since 1964, the Democratic candidate for president actually carried Salt Lake County. This happened with 31 percent of Utah whites backing Obama. Not even close to a winning margin; but in Louisiana, for example, Obama only won 14 percent of the white vote.
The reason, of course, for the lack of racial polarization in Utah is that it is overwhelmingly white. By contrast, states with large black populations (particularly those in the South) are often much more polarized along racial lines. Following up on my analyses of state-level Obama support by black population, I therefore plotted state-level GOP birther misperceptions against the state-level black population (with the aggregate US total added for context). While it is obviously far too early to draw any firm conclusions, the result is highly suggestive:
Again, the plot is only for illustrative purposes -- it is far too soon to tell if the relationship will hold with data from more states. But the fit to the state data is almost perfectly linear thus far (R2=.99).
Update 8/11 1:53 PM: Full results from the North Carolina poll are here (PDF).