[W]ho is Trump's base? White voters with less formal education, certainly -- that demographic now makes up 59 percent of GOP voters, from 50 percent in 2010, while whites with college degrees shrank from 40 percent of the GOP to 29 percent, the biggest shift happening from 2016 to 2018, Thomas Edsall writes in The New York Times. But according to research from political scientists Herbert Kitschelt (Duke) and Philipp Rehm (Ohio State), Trump's base isn't the "white working class," or lower-income white voters without college degrees, Edsall explains:

Instead, Kitschelt and Rehm find that the surge of whites into the Republican Party has been led by whites with relatively high incomes -- in the top two quintiles of the income distribution -- but without college degrees, a constituency that is now decisively committed to the Republican Party. According to the census, the top two income quintiles in 2017 were made up of those with household incomes above $77,552. ...

Low-income whites without college degrees have moved to the Republican Party, but because they frequently hold liberal economic views -- that is, they support redistributionist measures from which they benefit -- they are conflicted in their partisan allegiance. [Edsall, The New York Times]

Both groups of non-college white voters "tend to endorse authoritarian policies on the noneconomic dimension," Kitschelt and Rehm write, but the blue-collar non-college whites swung to Trump because they viewed him as "substantially more moderate than his party," mostly due to his pledge to protect Medicare and Social Security.