In a large, diverse country, campaigns span a broad array of interests and motivations. But the political foundation of Donald Trump's presidency was racial grievance.

Trump has repeatedly appealed to unhappy whites with his denunciation of Mexican immigrants, his defense of white supremacist protesters, and his attacks on black athletes protesting for racial justice. Thursday's Oval Office excoriation of "s---hole countries" in Africa and the Caribbean simply followed that pattern. (Trump appeared to deny making the comment on Friday, although some senators in the room at the time pushed back against him).

As a candidate and as president, Trump has sounded plenty of race-neutral themes, including the call for tax cuts that culminated in landmark legislation last month. But some political science research has shown that his blunt race-tinged messages were the reason he vaulted past an experienced lineup of rivals to win the 2016 Republican nomination and then the White House.

Emily Ekins, director of polling at the libertarian Cato Institute, identified five groups of Trump voters as part of a broader Democracy Fund study of the 2016 election. Key to his emergence, she concluded, was the 20 percent segment she called "preservationists," who stood out for their "nativist and ethno-cultural conception of American identity."

"American Preservationists comprise the core Trump constituency that propelled him to victory in the early Republican primaries," Ekins wrote.

She characterized them as having low levels of education, income and political information, watching lots of television, and offering strong professions of Christian faith combined with infrequent church attendance. With many of them disabled and on Medicaid, they display hostility toward Wall Street, support for redistribution of wealth, and concern about their government retirement benefits.

Their economic views help explain Trump's pledge not to touch Social Security and Medicare benefits. Their social views explain where they found kinship with him.

"They are far more likely to have a strong sense of their own racial ident