DETROIT (Reuters) - Democratic presidential front-runner Joe Biden and Senator Cory Booker traded accusations over their criminal justice records on Wednesday, with Booker calling the former U.S. vice president an “architect of mass incarceration” and Biden slamming Newark’s “stop and frisk” policing when Booker was mayor.

Democratic U.S. Presidential candidate Joe Biden addresses the audience during the Presidential candidate forum at the annual convention of the National Association of the Advancement of Colored People (NAACP) in Detroit, Michigan, U.S. July 24, 2019. REUTERS/Rebecca Cook

Booker, who has been lagging in the polls, criticized Biden’s new criminal justice plan and referenced his role as a U.S. senator in writing the 1994 crime bill, which critics say led to high incarceration rates that unfairly hit minorities.

“For a guy who helped to be an architect of mass incarceration, this is an inadequate solution to what is a raging crisis in our country,” Booker, who is black, told reporters after appearing at the annual NAACP convention in Detroit.

Biden responded that when Booker was mayor of New Jersey biggest city, its police department had a “stop and frisk” program that mostly targeted African-American men as officers stopped individuals to search them for weapons or illegal items.

“If he wants to go back and talk about records, I’m happy to do that,” Biden told reporters after speaking at the same convention. “But I’d rather talk about the future.”

Biden’s deputy campaign manager Kate Bedingfield later responded with a statement raising questions about Booker’s record as mayor of Newark, a majority African-American city he led from 2006 to 2013.

“The absurdity of this attack is obvious. Almost 90% of all people incarcerated in America are in state and local prisons and jails for violating state laws – laws that Joe Biden, of course, did not write,” she said.

Ten presidential candidates addressed the nation’s largest civil rights organization, a week before the second presidential debates in Detroit.

Democrats have intensified their efforts to win over black voters, one of the party’s most loyal constituencies, after the first decline in African-American turnout in 20 years in the 2016 election. That helped sink Hillary Clinton and contribute to Trump’s upset win.

Slideshow ( 13 images )

Neither Biden nor Booker directly attacked each other in their speeches at the convention, saving their criticisms for comments to reporters afterward.

BIDEN DEFENDS CIVIL RIGHTS RECORD

During his appearance, Biden defended his civil rights record and spoke about his close relationship with Barack Obama, the first black U.S. president.

“They did a significant background check on me for months with 10 people. I doubt whether they would have picked me if these accusations about me being wrong on civil rights were correct,” Biden said.

Biden’s early lead in the nominating contest has been fueled in part by strong support from black voters. But he has slipped in the polls since the first debate last month with U.S. Senator Kamala Harris, who criticized his opposition to federally mandated busing to integrate schools in the 1970s and his willingness to work with segregationist senators.

On Tuesday, Biden unveiled a criminal justice plan that reverses several elements of the 1994 crime bill he helped write.

“Every major initiative needs to be reformed,” Biden told the convention, calling the 1994 legislation a response to “a giant epidemic in America of violence,” particularly in African-American communities.

“We have now a systemic issue and too many African Americans in jail right now, so I think we should shift the whole focus from what we were doing in terms of incarceration to rehabilitation,” he said.

Biden’s new plan includes measures to end racial disparities in the criminal justice system, such as providing greater access to better public defenders, ending mandatory-minimum sentences and scrapping the cash bail system.

Booker said the new plan was too little, too late, however.

“For him not to have a more comprehensive plan to deal with this is unacceptable to me, especially because he is partially responsible for the crisis we have now,” he told reporters.

Delegates to the convention on Tuesday endorsed the impeachment of Republican President Donald Trump.

Trump declined an invitation to appear, telling reporters last week that was because the NAACP changed the date and format of his appearance. He wanted to give a speech, he said, but the group said he had to participate in the same question-and-answer format as the other candidates.