By checking 'black' as his race on the census form, President Obama is at odds with clear demographic trends toward multiracial pride. The number of Americans identifying as both white and black jumped 134% in 10 years. It could have been a historic teaching moment. Instead, President Obama, the most famous mixed-race person in the world, checked off only one race — black — last year on his census form. And in so doing, he missed an opportunity to articulate a more nuanced racial vision for the increasingly diverse country he heads. The president also bucked a trend. Last month,...