The vice president’s office also said Mr. Biden had played a “critical” role in the Obama administration’s continuing efforts to overhaul the system, meeting with members of Congress and participating in “high-level staff discussions.”

In a sign of the shifting mood, former President Bill Clinton, who long viewed the crime legislation as a major achievement of his administration, told the national convention of the N.A.A.C.P. in July that it in fact went too far in toughening sentencing standards and thus contributed to mass incarceration, a once controversial term now widely used.

“I signed a bill that made the problem worse,” Mr. Clinton said. “And I want to admit it.”

Despite reservations, Mr. Biden, who has served as the Obama administration’s unofficial liaison to the law enforcement community, has not only stood by the 1994 legislation, but has also frequently taken credit for it. As recently as this spring, in an essay on community policing for a book of bipartisan reform proposals put together by the Brennan Center for Justice, Mr. Biden referred to the legislation as the “1994 Biden Crime Bill.”

Mr. Clinton wrote in a foreword to the book that “our nation has too many people in prison and for too long — we have overshot the mark.” Mr. Biden, in contrast, stressed the success of the bill’s community policing measures, which he said had achieved their goals before funding was cut.

And in an interview with Time magazine in February 2014, he said, “I am not only the guy who did the crime bill and the drug czar, but I’m also the guy who spent years when I was chairman of the Judiciary Committee and chairman of [the Senate Foreign Relations Committee] trying to change drug policy relative to cocaine, for example, crack and powder.”

Activists say it would take an acknowledgment by Mr. Biden similar to Mr. and Mrs. Clinton’s to begin to get the ear of the young minority voters so crucial to Mr. Obama’s coalition.