Former Vice President Joe Biden and Senator Cory Booker of New Jersey fought hard over criminal justice reform at Wednesday evening’s Democratic debate in Detroit.

“There’s a saying in my community,” Booker quipped. “You’re dipping into the Kool-Aid and you don't know the flavor.”

Booker’s pointed attack on Biden centered on Biden’s self-described role in shepherding Senate legislation in the 1990s that stiffened some criminal penalties and increased federal prison populations.

“There are people in prison right now for drug offenses because you stood up and used that tough on crime rhetoric that got a lot of people elected but destroyed lives in communities like mine,” Booker charged.

Biden returned fire with a focus on Booker’s eight years as the mayor of Newark, where, Biden said, “you hired Rudy Giuliani’s guy and engaged in stop and frisk,” a reference to Garry McCarthy, the former number-two official at the New York Police Department.

The back-and-forth highlighted divides not just between Booker and Biden, but larger ideological and generational fissures that have split the sizable field of Democratic candidates on other issues like health care and immigration.

Biden has drawn significant flack from Democratic rivals over his past positions on criminal and racial justice issues in particular, and his long tenure—and voting record—as a senator have provided opponents with plenty of material to try to chip away at his progressive appeal.

“If you want to compare records [on criminal justice], and frankly I’m shocked that you do, I’m happy to do that,” Booker told Biden during their exchange.

Biden has countered by invoking his tenure in the administration of the nation’s first black president, and intimated that Booker had simply signed his name to Obama-era criminal justice legislation negotiated by the administration.

The exchange was prompted by comments Booker made a week earlier, when he described a criminal justice reform plan released by the Biden campaign as “inadequate” and dubbed him “an architect of mass incarceration.”

“Since the 1970s, every crime bill, major and minor, has had his name on it,” Booker said. “The house was set on fire, and you claimed responsibility for those laws, and you can't just come out now and put out that fire.”