Former President Bill Clinton engaged in a heated exchange on Thursday with protesters upset about welfare reform and gun violence laws passed when he was in office 20 years ago.

Addressing supporters at a Hillary Clinton presidential rally in Philadelphia, Bill Clinton was interrupted by people in the crowd holding signs reading "Clinton crime bill destroyed our communities" and "Welfare reform increased poverty."

As first lady, Hillary Clinton said in a 1996 speech about the crime bill, "They are often the kinds of kids that are called super-predators." Some blacks have found the term "super-predators" offensive and have tried to hold her accountable during her presidential campaign. She was interrupted at a rally in Charleston, S.C., in February by an activist who wanted her to apologize for her remarks.Critics of the 1994 anti-crime bill have tied it to mass incarceration disproportionately affecting blacks. Bill Clinton said he talked at the time to black groups, which endorsed the legislation, and he said the bill led to a decrease in crime and murders due to gun violence.

"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 on the street to murder other African-American children," Bill Clinton told the crowd. "Maybe you thought they were good citizens. She didn't. You are defending the people who killed the lives you say matter. Tell the truth."

DEM 2016 Bill Clinton

Protester Rosco Farmer is corralled in the back of the auditorium by civil affairs officers near the end of former President Bill Clinton's speech during a rally for Democratic presidential candidate Hillary Clinton. (Ed Hille/The Philadelphia Inquirer via AP)

Clinton, a Democrat, said that the majority of people serving disparate sentences for crack cocaine are in state prisons and jails. He said that President Barack Obama, also a Democrat, is working to release federal prisoners serving unfairly lengthy sentences.

"Who do you think those lives were that mattered?" Clinton asked the protesters. "Whose lives were saved that mattered? Hillary didn't vote for that bill, because she wasn't in the Senate."

Hillary Clinton is battling Vermont U.S. Sen. Bernie Sanders for the Democratic presidential nomination. Their contest, with accusations of lying, hustling for money and failed leadership, has taken a decidedly negative turn, and they recently have exchanged a series of barbs over qualifications for the presidency.