Fresh off an overwhelming victory in South Carolina’s Democratic primary, President Biden rallied supporters on Sunday in Nevada, saying that he had kept his promises to the Black and Hispanic voters who helped elect him.

Mr. Biden spoke at a community center in the historic Westside neighborhood of Las Vegas, home to an African American community in a critical battleground state. He rattled off statistics about reductions in child poverty for Black, Hispanic and Indigenous people, talked about growth in minority-owned business and attacked former President Donald J. Trump for saying that immigration was “poisoning the blood” of the United States.

But he seemed to acknowledge that many voters were skeptical of his accomplishments as president at a time when his approval rating had sunk below 40 percent

“I know, we know, we have a lot more to do,” Mr. Biden said. “Not everyone is feeling the benefits of our investments and progress yet.”

The president has been working to shore up his support among Black and Hispanic voters, who make up key Democratic constituencies, as Mr. Trump, his likely Republican opponent in November, tries to make inroads among both groups.

Nevada will hold its Democratic primary on Tuesday, the party’s second official nominating contest after South Carolina. But Mr. Biden faces scant opposition here. One long-shot challenger, Representative Dean Phillips of Minnesota — who finished third in South Carolina on Saturday, behind the self-help author Marianne Williamson — will not even be on the ballot.