“Look, it’s not a new conversation for me. In fact, it’s a conversation that’s come up every single time in every election that I have — and here’s the operative word — won,” she said. Her largely white audience liked the pitch, responding with rapt silence and then with raucous applause when she talked candidly about her own accomplishments.

For years, prospective Democratic nominees came to Iowa to talk ethanol and pork subsidies and saved any rhetoric about the injustice of racial profiling for crowds in South Carolina and Nevada — the only early voting states where black and Latino voters made up a significant portion of the Democratic electorate.

But in the era of Mr. Trump, and after social movements such as Black Lives Matter pushed racial inequality to the forefront of national politics, it’s white Democrats in Iowa and New Hampshire — not black ones in South Carolina — who, to this point, are embracing the candidates who promise to upend society in the name of racial equity.

Former Vice President Joseph R. Biden Jr. has held a commanding lead in national polls with nonwhite Democrats, but surveys show that white liberals in Iowa and New Hampshire are less inclined to support him. At events for Mr. Biden , some white voters cite his confounding September debate answer on the legacy of slavery and previous Senate work with segregationists as reasons to support other candidates.

At events for Senator Elizabeth Warren of Massachusetts, and Pete Buttigieg, the mayor of South Bend, Ind. — two white candidates who have particularly excelled with college-educated liberals — supporters pointed to policies addressing racial inequalities as part of the candidates’ appeal.

These policies may give cover to those seeking to support a white candidate in a historically diverse Democratic field, which includes Ms. Harris, Senator Cory Booker of New Jersey, and former cabinet secretary Julián Castro — candidates who are themselves racial minorities and who are struggling to gain traction in the polls.

“My daughter is marrying an Asian man and diversity has become very important to me,” said Julie Neff, a 57-year-old Iowa Democrat who attended the Harris rally. Ms. Neff, who is white, said she was embarrassed that she started thinking about race and discrimination only later in life.