The groans erupted halfway through Bernie Sanders’s appearance Wednesday at a presidential candidates’ forum sponsored by She the People, a group that aims to drive up voter participation among women of color.

Before an audience of about 1,700, many of them African American and Hispanic women, the moderator asked Sanders (I-Vt.) how he would handle the rise in white supremacy. Sanders spoke of fighting discrimination and running a campaign “to bring our people together around an agenda that speaks to all people” — then returned to a familiar message on universal health care.

For many in the audience, that was insufficient. “Come on!” a woman shouted from the back, as others began to jeer and boo.

The reception reflected Sanders’s struggle to win support from minority voters, a problem that dogged his 2016 primary campaign against Hillary Clinton.