The evidence that racial attitudes now play an important role in vote choice among white voters is overwhelming. It has been replicated in study after study, in just about every major survey in political science over the last decade.

If you wanted to know whether white Obama voters would support Mr. Trump in 2016, you were better off knowing their demographics and answers to questions about race than knowing their political ideology, like whether they considered themselves conservative. You were better off knowing their attitudes about race than whether they were anxious about their economic situation, whether they had a college degree, or their age or gender.

Many white Americans have long held what political scientists call conservative racial views, like believing that African-Americans struggle to get ahead because they don’t work hard enough, rather than because of discrimination or the legacy of slavery.

But these attitudes were often latent in electoral politics. More than a decade ago, a majority of less educated white voters did not perceive a major difference between the two parties on racial issues, according to Mr. Tesler’s research. And most campaigns weren’t overtly trying to disabuse them of that notion.

Now, some white voters, especially less educated ones, see a bigger difference between the two parties on racial issues. They saw Mr. Trump as far more conservative on immigration. They believed Hillary Clinton was much likelier than Donald J. Trump to support increased aid to African-Americans. They thought that of John Kerry and Mr. Obama too, but not by nearly as much.

More than anything else, the rising salience of race helps explain which white voters defected to vote for Mr. Trump in 2016 and which did not. It even helps make sense of why white voters without a degree swung toward Mr. Trump, but white voters with a degree did not.

White voters began to see the parties through a more racialized lens with the election of Mr. Obama in 2008. The Obama presidency made many traditionally Democratic and often less educated white voters aware of the Democratic Party’s alliance with black voters; it implicitly called into question whether the party was for them.