Titled "An Urgent Conversation with the American People," the multi-hour, livestreamed discussion came ahead of Congress' return to session on Monday.
"The reason I'm standing here today is because I got back up. I fought back," Sen. Elizabeth Warren said.
Ten Democratic candidates will gather at Texas Southern University in Houston for the third Democratic presidential debate on Thursday.
Protesters were demanding New York Mayor Bill de Blasio fire the police officer accused of using a fatal chokehold on Eric Garner.
Ten candidates, including Elizabeth Warren, Cory Booker, Julian Castro and Beto O'Rourke, converged on stage in Miami Wednesday for the first Democratic candidate debate.
Democratic presidential candidate Joe Biden is dismissing calls to apologize for saying that the Senate "got things done" with "civility" even when the body included segregationists with whom he disagreed.
