DETROIT — Joseph R. Biden was the floor general for the crime bill as it moved through the Senate in 1993, imploring his fellow lawmakers to “take back the streets” from thugs who had imperiled the safety of average Americans.

The violent drug trade and surging homicide rates demanded more police and stiffer sentences, said Mr. Biden, then a senator from Delaware, and it didn’t matter whether those committing the crimes were “deprived as a youth” or “victims of society.” Justice was the order of the day.

Nearly two decades later, that bill has earned Mr. Biden blame as the jailor of a generation of black men or, as Black Lives Matter activist Shaun King put it, the “Father of Mass Incarceration.”

Mr. Biden is grappling with the issue as he battles to become the 2020 Democratic presidential nominee, facing off against a younger generation of contenders who say their elder statesman is the reason the nation’s correctional system — which includes people in prison and jail, on parole and probation — expanded from about 3 million in 1985 to 7.1 million just two decades later.

But the situation is far more complicated than that.

The vast majority of those who ended up behind bars over the past 15 years were in state jails and prisons, far from the reach of Mr. Biden’s crime bill, and the state numbers show the get-tough consensus extended far beyond Capitol Hill.

“I feel like the conversation has been distracted,” said Inimai M. Chettiar, policy director of the Justice Action Network and former director of the Brennan Center’s Justice Program. “It starts with understanding that just about anyone who was an adult in the ‘90s was supporting mass incarceration because that is where the politics were.

“I guess the long and the short is that it is not as simple as people are trying to make it,” she said. “It is not that the crime bill was the cause or not the cause.”

Former Virginia Gov. George Allen said Mr. Biden was definitely not on his mind in 1994 when he formed a commission — co-chaired by William Barr, fresh off his first stint as U.S. attorney general — to come up with a better crime policy.

Mr. Allen ran for election in 1993 on a platform of abolishing parole, and his commission added other sentencing changes to the mix, targeting repeat criminal offenders with stiffer penalties.

“We in Virginia were controlling our own destiny and making Virginia safer,” Mr. Allen said. “We weren’t going to wait for the federal government to act.”

Washington state started the movement with a truth-in-sentencing law in 1984, and five others followed in the early 1990s. In North Carolina, lawmakers were prodded to action by the shocking killing of basketball star Michael Jordan’s father.

By the middle of the 1990s, Virginia and 10 other states added their own stricter sentencing guidelines.

Mr. Allen said the changes in Virginia helped reduce recidivism rates.

He also said the blowback against Mr. Biden and tough-on-crime lawmakers is coming from “criminal apologists who are looking at ways to apologize for criminals because of the trauma of bottle-feeding or potty-training as a kid.”

“He is getting swept up in this new rage, where they think everyone in prison is Merle Haggard and just a wayward person who can be turned around, and hopefully and prayerful that is the case, but a community has the right to set the parameters for people convicted of violence against fellow human beings,” Mr. Allen said.

There is no question the changes at the state and federal levels led to more people behind bars.

State prison populations jumped from about 450,000 in 1985 to nearly 1 million a decade later. By 2005, the number was approaching 1.3 million. In 1985, white prisoners made up slightly more than black prisoners in the states. That had reversed by 1995, when black prisoners slightly outnumbered white inmates.

But because whites make up far more of the U.S. population, that small increase in ratio within prisons translates to a large increase in the percentage of black Americans serving sentences.

At the federal level, prison populations were increasing even before President Clinton signed the Violent Crime Control and Law Enforcement Act. The federal prison population jumped from 24,000 to 95,000 from 1980 to 1994, according to the Federal Bureau of Prisons. It reached a peak of 219,000 in 2013 and has since fallen to 177,000.

One reason the law gets blamed for the nationwide increase in prisoners is the $30 billion fund it included to pay for more local police and billions of dollars more in grants to encourage states to build more prisons, to expand drug testing and to enact truth-in-sentencing laws.

A 2001 analysis from the Rand Corp. think tank, though, found that “in only four states was the receipt of federal grant funds a major factor in passing [truth-in-sentencing] laws, but most [truth-in-sentencing] states would probably have passed [truth-in-sentencing] legislation anyway.”

Supporters of the crime bill in the 1990s included then-Reps. Bernard Sanders of Vermont and Jay Inslee of Washington, a pair of 2020 presidential contenders.

Mr. Sanders said he voted for the bill because it included the Violence Against Women Act, not because of the tough-on-crime elements and restrictions on assault weapons. Mr. Inslee says he regrets his vote because it led to racial disparities in the system.

Reps. Nancy Pelosi of California, Steny H. Hoyer of Maryland and James E. Clyburn of South Carolina, now the top Democrats in the House, opposed the effort.

But it is Mr. Biden who, with Mr. Clinton, is most closely tied to the bill, with his warnings of rampant crime and his dismissal of attempts to explain away the motives of criminals.

“The end result is they are about to knock my mother on the head with a lead pipe, shoot my sister, beat up my wife, take on my sons,” Mr. Biden said in a video that has been widely circulated online during the 2020 campaign. “So I don’t want to ask what made them do this. They must be taken off the street.”

At the bill signing ceremony, Mr. Biden received a round of applause after Vice President Al Gore singled him out for special recognition, saying he had fought “tirelessly” for the legislation for six years.

Mr. Biden wore the law as a badge of honor and particularly claimed ownership of the increase in police officers.

He also claims credit for drug courts, which were a part of the law, encouraging diversion of some drug offenders out of the prison system, and the Violence Against Women Act.

But in a recent speech in South Carolina, Mr. Biden said the problems the law created were out of his hands.

“I didn’t support the provision the president wanted, ‘three strikes and you’re out.’ Didn’t support it then, don’t support it now. I didn’t support any mandatory minimums. I didn’t support more money to build state prisons,” he said. “I supported the bill. I will accept responsibility for what went right, but I will also accept responsibility for what went wrong.”

Now, as Mr. Biden’s legacy on race is under scrutiny, the crime bill is receiving renewed attention — at least among politicos.

Sen. Cory A. Booker of New Jersey, another 2020 candidate who has championed sentencing reform, blames the law for a massive expansion of incarceration.

“From the time I was in law school to the time I was mayor of the city of Newark, we were building a new prison or jail every 10 days in America while the rest of our infrastructure crumbled,” he says. “That bill was awful.”

It’s not clear, however, that voters care. Mr. Biden remains the top choice of voters from the black communities that activists say were hurt the most by his efforts.

The Rev. Al Sharpton, who opposed the law, said the biggest problem for Mr. Biden is that he used to tout the crime bill as a major accomplishment. The former senator and vice president, as recently as a few years ago, called it the “Biden Crime Bill” and touted its increase in police.

“And it worked,” Mr. Biden said in 2015.

More recently, Mr. Biden has sought to put political distance between himself and the crime bill.

Last week, he rolled out a plan to overhaul the criminal justice system that seeks to reverse parts of the bill that have caused him headaches.

Among other measures, Mr. Biden is calling for legislation to limit federal mandatory minimum sentences to the highest-level drug offenders and to reduce prison sentences through good behavior.

His plan also would create a $20 billion grant program that would give incentives to states to craft their own policies to reduce incarceration rates, including by eliminating mandatory minimum sentences for nonviolent crimes.

Mr. Sharpton, speaking before Mr. Biden’s latest proposal, said the former vice president’s attempts at distance ring hollow. Still, Mr. Sharpton cuts Mr. Biden some slack, saying the times must be reckoned with.

“In fairness to Joe, most of the Congressional Black Caucus was for the crime bill,” said Mr. Sharpton, noting that the 1986 death of All-American basketball star Len Bias from cocaine helped fuel the fire. “People were apoplectic.”

“The facts get twisted because the crime bill was federal, and where we started seeing a lot of the incarceration rates blossom out of control was at the state level, which was not caused by the 1994 crime bill,” he said.

“As much as I was against it then, and against it now, that did not cause the prison industrial complex,” he said. “It was more [at] the state level.”