‘Birtherism’ is on the decline following the release of the President’s long form birth certificate. But it is nonetheless instructive to consider how the meme was accepted by so many conservatives. Alan I Abramowitz has what is likely be the definitive data-driven post on the subject up at Larry J. Sabato’s Crystal Ball. Abramowitz weighs the data regarding the influence of partisanship, ideology and race on formation of the birther meme:

Until now, debates about the influence of racial attitudes on opinions of Obama have been severely hampered by a lack of survey data including relevant questions. However, the availability of a new data set now makes it possible to directly examine the impact of racial attitudes on whites’ evaluations of President Obama.
The data used in this article come from the October 2010 wave of the American National Election Study Evaluations of Government and Society Survey (EGSS). The October 2010 survey was the first of several cross-sectional studies being conducted by ANES in 2010, 2011 and 2012 to test new instrumentation and measure public opinion between the 2008 and 2012 presidential elections. The surveys are being conducted entirely on the Internet using nationally representative probability samples. Respondents are members of the Knowledge Networks KnowledgePanel, an omnibus panel of respondents recruited using telephone and address-based sampling methods who are provided free Internet access and equipment when necessary.
Evaluations of President Obama were measured by two questions, a five-point scale measuring positive versus negative feelings about the president and a seven-point scale measuring how strongly respondents liked or disliked him. The correlation between these two questions was a very strong .85, so I combined them into a single Obama rating scale with a range from 0 (extremely negative) to 10 (extremely positive). The mean score on this scale was 5.1 with a standard deviation of 3.6. About a third (34%) of respondents gave Obama a rating of 8 through 10 while 31% gave him a rating of 0 through 2. Thus, opinions of Obama were closely divided and highly polarized.

Abramowitz also notes that “Obama’s approval rating averaged 38% for whites compared with 59% for nonwhites including 85% for African Americans.” Turning to the question of ‘birther’ attitudes, Abramowitz examines the data and adds,

…Racial resentment had a strong impact on beliefs about his place of birth. While recent polling indicates that doubts about whether President Obama was born in the United States have diminished since he released his “long form” Hawaiian birth certificate, the “birther” myth has proven stubbornly resistant to evidence. In fact, 58% of white respondents in the EGSS expressed some doubt about whether Barack Obama was born in the United States including 28% who thought that he definitely or probably was not born in the United States.

Abramowitz concludes that “partisanship and ideology were the strongest predictors of overall evaluations of President Obama and opinions about his place of birth among white Americans” and that “regardless of party or ideology, whites who scored high on racial resentment had more negative opinions of Obama and were more likely to harbor doubts about whether he was born in the United States than whites who scored low on racial resentment.”
Given the tenacity of racial bias among a substantial segment of the public, President Obama’s approval ratings are all the more impressive, as is his ability to calmly navigate around the treacherous shoals of race in America.