The graph above shows the relationship between support for interracial dating and whites’ support for Democratic presidential candidates in 2004, 2008, and 2012. Whites who opposed interracial dating (roughly 20 percent) were significantly less likely to support Obama in 2012 and 2008 than the Democratic presidential candidate in 2004.

At the same time, about one quarter of whites who didn’t even think blacks and whites should date each other still supported Obama for president. An analysis by political scientists Sam Popkin and Doug Rivers showed the same thing: 20-25% of whites who opposed interracial dating supported Obama throughout the 2008 campaign.

Even though racial attitudes were a bigger factor in Obama’s elections than previously, they were by no means the only factor. The most important determinant of Americans’ votes in 2008 and 2012, as always, was party identification.

But until Obama’s presidency, there were nearly as many white Democrats with explicitly prejudiced views as white Republicans. That meant that lots of racially prejudiced Democrats wound up supporting Obama.