Age within different demographic groups isn't uniformly distributed, right? We'd be at the point when boomers are approaching end of life, but there wasn't an equivalent nonwhite boom, iirc.

I also suspect that the idea of whiteness has long held itself to be culturally exclusive ("you are not white if one of your parents is Black") while other racial groups are the inverse. There's a... lot of baggage and history there obviously. But I could see the manner in which the census asks about race being skewed by our cultural understanding of our race.

I also believe that wealthier, more educated folks tend to have fewer children. Which could suggest that, in the US white folks have more access to wealth and education.

Which is a long winded way of saying racial demographics is complicated and I can imagine many reasons why groups might rise or decline that are way less sinister than they are the enemy of the state.