The former vice president's campaign is looking at South Carolina, where African Americans make up a large share of the electorate, as a must-win state.
Sen. Bernie Sanders won narrowly, but can he expand his base? Pete Buttigieg again did well, but in another largely white state. And the story of the night was Sen. Amy Klobuchar's third-place finish.
The victory, projected by the Associated Press, comes in another close race with Pete Buttigieg, former mayor of South Bend, Ind. The two had a virtual tie atop the Iowa caucuses.
The remarks, shared widely on social media this week, have sparked discussion about the former New York City mayor's past support of stop-and-frisk policies, which targeted minority neighborhoods.
The top target is Pete Buttigieg. He faced a barrage of attacks as the other Democratic candidates seek to blunt his momentum from a strong showing in Iowa.
Sen. Bernie Sanders easily beat Hillary Clinton in the state in 2016, and likely has the progressive vote locked up. Fellow Iowa caucus winner Pete Buttigieg wants to claim the mantle of electability.
Many politicians are skeptical about the power of their endorsement, but that's not slowing the pace of announcements ahead of Tuesday's primary in New Hampshire.