Former vice president Joe Biden speaks at a campaign event earlier this month. (John Locher/AP)

Former vice president Joe Biden, who has faced criticism from liberals for spearheading a 1994 law when he was a senator that some view as unduly harsh, announced a proposal Tuesday that would eliminate the death penalty and attempt to undo some of the impacts of the legislation he championed a quarter-century ago.

The plan is Biden’s latest bid to appeal to the liberal activists who have dominated the crowded Democratic field, and yet another indication that the centrist, return-to-normalcy candidate is trying to shift the focus toward his vision for the future and away from decades-old positions that may no longer be politically popular in the party.

Biden in recent weeks has also shed his career-long opposition to federal funding for abortions and has come out in favor of a public insurance option on health care. The positions put him in a space that is more liberal than he — and most of the Democratic Party — have occupied in the past, though still far from the fringes of the current presidential field.

Polling suggests that in some cases, Biden is taking positions that have broad support, and Democrats so far have been forgiving of Biden’s willingness to shift with the times.

The former vice president’s moves on criminal justice appear designed in part to head off a major confrontation at the next Democratic primary debate next week, where his record is expected to come under renewed scrutiny following a lackluster performance in the first debate. His support for the 1994 crime bill has been criticized by both Republicans and Democrats, who argue that it led to mass incarceration and tilted the system unfairly against African Americans.

Sens. Cory Booker (D-N.J.) and Kamala D. Harris (D-Calif.) — who are both African American — have been particularly critical of Biden’s record, and they will be standing on either side of Biden during the second night of next week’s debates in Detroit.

Booker tweeted a criticism of Biden’s new crime policy shortly after it was released Tuesday. “It’s not enough to tell us what you’re going to do for our communities, show us what you’ve done for the last 40 years,” Booker wrote on Twitter. “You created this system. We’ll dismantle it.”

Booker elaborated later in the day, saying, “The proud architect of a failed system is not the right person to fix it.”

Harris, whose campaign gained steam last month after she attacked Biden’s lengthy record of opposing mandated busing programs as a way to integrate schools, has also criticized Biden’s criminal justice record. She and other critics have seized on such provisions as the “three strikes” measure dictating long sentences if a convict has three offenses, even relatively minor ones.

“I have a great deal of respect for Vice President Joe Biden, but I disagree with him,” Harris said earlier this year. “That crime bill — that 1994 crime bill — it did contribute to mass incarceration in our country. It encouraged and was the first time that we had a federal three-strikes law. It funded the building of more prisons in the states.”

The proposal Biden outlined Tuesday aims to pass legislation abolishing the death penalty at the federal level and offer incentives to states to follow suit. Convicted criminals who would face execution under current law would instead be sentenced to life in prison without parole.

Biden’s plan also would decriminalize marijuana and expunge past cannabis-related convictions; end the disparity between sentences for powder and crack cocaine; and do away with all incarceration for drug use alone. In addition, it would create a $20 billion grant program to spur states to move from incarceration to crime prevention and would eliminate mandatory-minimum sentences.

Attitudes about race and criminal justice have changed considerably over the years in both parties, along with a significant drop in crime rates. Democrats in particular have moved away from policies that empower police and prosecutors, instead committing to addressing inequities that they say have damaged minority communities.

Biden’s criminal justice platform will face an especially important test in black communities. He is seeking to appeal strongly to African Americans, whose votes will play a big role in the primary. Biden is popular in the black community, but his previous support for tough-on-crime policies could be a vulnerability there.

At a campaign visit Tuesday to a program for underserved youth in New Orleans, he spoke mostly about his childhood experiences on the predominantly black side of Wilmington, Del., without making any overt references to the criminal justice plan he had rolled out just hours earlier.

For Biden, a longtime advocate of capital punishment, the decision to oppose the death penalty represents a particularly notable change. The former senator from Delaware gave a speech in 1992 in which he boasted that a crime bill he helped draft included 53 death penalty offenses.

“Weak as can be, you know?” he added in a sarcastic response to critics who said the bill was too soft. “We do everything but hang people for jaywalking in this bill.”

Biden’s new plan says, “We need to confront racial and ­income-based disparities in our justice system and eliminate overly harsh sentencing for nonviolent crimes.” To that end, it proposes extending the power of the Justice Department to attack systemic misconduct in police departments and prosecutors’ offices.

Biden’s proposal also calls for ending cash bail and terminating the federal government’s use of private prisons. And it includes a provision to ensure that people who are imprisoned are treated humanely.

One area in which he differs with other Democrats is marijuana. While Biden’s plan would decriminalize its use as a recreational drug, he stops short of legalizing its use, while other candidates support legalization. That is similar to other issues on which Biden has moved toward more liberal positions without going as far as other Democratic candidates.

A Marist Poll released this week illustrates the political backdrop for these moves. It showed that 70 percent of adults hold positions similar to Biden’s on health care — allowing Americans to choose between public or private insurance — while 41 percent support a plan being pushed by other leading candidates, including Sens. Elizabeth Warren and Bernie Sanders, to replace private health insurance with a Medicare-like plan for everyone.

The survey also showed little support for decriminalizing illegal border crossings and providing reparations for slavery, positions that Biden has opposed but that others in the field have supported.

In general, Biden has attempted to focus attention on his eight years as vice president in the Obama administration. But he has a four-decade political record that his rivals cast as out of step with modern times.

Few issues have been as central to that dance than his role in pushing tough-on-crime legislation that culminated with the 1994 crime bill. His language in the early 1990s grew increasingly provocative, particularly about repeat offenders who he called “predators in our streets.”

“It doesn’t matter whether or not they were deprived as a youth,” Biden said on the Senate floor during a 1993 debate. “It doesn’t matter whether or not they had no background that enabled them to become socialized into the fabric of society. It doesn’t matter whether or not they’re the victims of society. The end result is they’re about to knock my mother on the head with a lead pipe, shoot my sister, beat up my wife, take on my sons.”

The 1994 bill was Biden’s most ambitious tough-on-crime effort in the Senate by far. Though it delivered liberal priorities such as his Violence Against Women Act, it also created a federal “three-strikes” rule, applied the death penalty to 60 new offenses, funded 100,000 new police officers and offered states money to construct prisons in exchange for abolishing or tightening parole.

It unfolded during a very different time, when violent crime was a significant concern of many Americans in a way it isn’t today. The legislation had the support of President Bill Clinton, and a majority of the Congressional Black Caucus voted in favor.

“My constituents, both in the city and in suburban Chicago, were beside themselves about crime and how vicious the streets seemed to be,” Carol Moseley Braun, an Illinois Democrat who supported the bill as the Senate’s only black member, said in an interview. “In hindsight, maybe a lot of that was overblown. But hindsight is 20/20.”

Elise Viebeck, John Wagner and Amy B Wang contributed to this report.