> This perception is mistaken: https://academic.oup.com/qje/article/135/2/711/5687353

That paper covers the period 1989 to 2015. I based my idea that non-black minorities become "white" partly on the realization that in recent decades hispanic populations have integrated quite well, and are a growing Republican constituency. And I came to that opinion in the very early 2000s. (If not earlier--I distinctly remember mentally critiquing the assumption that both Francis Fukuyama and Samuel Huntington made in their late 1990s books regarding the political effects of a future hispanic-heritage majority.) I'm a [late] Gen X'er who grew up in the Midwest and Deep South and from my perspective hispanic culture and identity was already going mainstream, to the extent it was even distinguishable as alien. By contrast, almost all the adults in my community quite clearly held strongly and uniformly to old, persistent stereotypes of hispanics.

If you look at hispanic mobility over previous eras, I'm pretty sure it would look different. (Though I could be wrong--I don't recall seeing hard data, just plenty of anecdata, including centuries of received cultural narratives.) That historical disparity and relatively slow integration is presumably why older scholars just assumed a growing hispanic population would lead to a cultural and political shift. And that old scholarship still influences modern assumptions among the liberal intelligentsia. But, of course, the fact that their mobility is now much like that of whites (notwithstanding a relative decrease in white mobility as compared to earlier eras) is evidence that whiteness is sufficiently adaptive and inclusive to forestall the racial reckoning--i.e. between white and black identities--that Americans have been facing for centuries.

In many ways the liberal achievements of the Civil Rights era sowed the seeds of its own political destruction. Not simply because it pissed off a bunch of white people leading to Nixon's infamous Southern Strategy, but because it opened the doors of economic and, more importantly, cultural opportunity to Latinos and Asians, much more so than for African Americans. With those two large (and growing) groups increasingly knitted into the fabric of the American white mainstream, much like the Irish, Italian, and slavic groups in earlier decades, there's less pressure to maintain the social efforts regarding the cultural, political, and economic enfranchisement of African Americans.

While not quite the same, I see many parallels with sex and gender equality, too. Anyone who thought the enfranchisement of women would bring a substantially liberal turn in American politics 1) never paid attention to the Temperance movement in history class, and 2) never took a peek inside a church to see who was sitting in the pews.

As I grow older I've come to better appreciate the critiques of mid-century African American writers: prejudice and racism is fundamentally about power.[1] One not-so-obvious consequence is that empowering the disenfranchised is more likely to lead to the once disenfranchised adopting and adapting prevailing prejudices than for those prejudices to be fundamentally overturned, simply because the salient effect of those prejudices is to preserve power by distinguishing the powerful. You could even see this with the gay marriage debates--it was astonishing how quickly gay culture began espousing what were once "heteronormative" ideas about relationships and family matters as gay marriage became more mainstream, often leaving their bi- and trans-gender allies in the lurch.

[1] No need to get into the specifics of what power means or the mechanics of how it manifests. I certainly have no sympathies for Marxist philosophies. I think many writers on racial and sexual equality gravitated toward Marxism because Marxism provided a vocabulary for discussing power. But it was the wrong vocabulary, and the dissonance is rather apparent in hindsight. Which isn't to say there isn't a huge overlap between racial and class power struggles. See, e.g., https://www.commondreams.org/author/adolph-reed-jr