Former President Bill Clinton slammed a Black Lives Matter protest against Hillary Clinton’s candidacy, and said the group defends gang leaders who get kids “hopped up on crack.”

“I don’t know how you would characterize the gang leaders who got 13-year-old kids hopped up on crack and sent them out into the street to murder other African American children—maybe you thought they were good citizens,” Clinton said.

“She [Hillary] didn’t. She didn’t. You are defending the people who kill the lives you say matter. Tell the truth.”

The angry response from the former U.S. president — his wife’s top surrogate — is sure to complicate matters for the Clintons as the contentious Democratic primary between Hillary Clinton and Vermont Sen. Bernie Sanders heads to the New York and then afterwards to Pennsylvania.

In both states, Democrats depend on the black vote in inner cities of New York and Philadelphia to win—and it’s been something the Clintons have had reliably under control until now.

Sanders is infuriating Hillary Clinton, she revealed in a Politico interview recently, because he refuses to go away and keeps winning states by large margins. If Sanders can gain traction in the inner cities and black communities that have been until now Clinton strongholds, he may be able to give Hillary Clinton a run for her money in the Empire State—a state that previously sent her to the U.S. Senate after Bill Clinton’s presidency ended—and in other states like Pennsylvania.