Joe Biden and Cory Booker are locked in a war of words over who is more responsible for putting too many black and brown Americans behind bars.

On Wednesday at the NAACP convention in Detroit, Booker accused the former vice president of being the “architect of mass incarceration.”

Biden shot back: “Cory knows that’s not true,” he told reporters in Detroit, according to CBS News.

Then Biden slammed Booker’s record in Newark, saying the former mayor allowed police officers to “stop and frisk” and the Obama Administration had to put a stop to the policy that was adversely affecting African American men.

The tit-for-tat happens just days before the second Democratic presidential primary debate in Detroit where Biden is expected to once again face criticism for his past policies that have since grown out of step with the younger, progressive Democrats.

Sen. Kamala Harris took aim at Biden at the first debate in a viral video moment for not doing enough to support school busing integration, which affected students like her.

The latest crime bill dispute started Tuesday when Biden released his criminal justice plan that reverses several provisions of the 1994 crime bill he helped write as a Delaware senator. The tough-on-crime legislation has become toxic on the left and blamed for widespread imprisonment of racial minorities.

Biden’s plan would fully end the sentencing disparities between powder and crack cocaine, end mandatory minimum sentences and eliminate the death penalty.

Booker pounced on the plan saying Biden is the “proud architect of a failed system is not the right person to fix it.”

Booker said the 1994 crime bill “inflicted immeasurable harm on Black, Brown, and low-income communities” and Biden’s plan “falls short of the transformative change our broken criminal justice system needs.”

He turned up the heat in Detroit on Wednesday at the NAACP convention where both candidates were speaking at a candidate forum.

Later Wednesday, Biden’s duty campaign manager Kate Bedingfield put out a campaign memo accusing Booker of running a police department “that was such a civil rights nightmare that the US Department of Justice intervened.”

“It is Senator Booker, in fact, who has some hard questions to answer about his role in the criminal justice system,” Bedingfield wrote, citing Booker’s support of a “zero tolerance policy” that put many people in the criminal justice system.

Booker and Biden will take the same debate stage on July 31.