A 22-year-old crime law is once again making news.

At a rally on Thursday, Bill Clinton confronted Black Lives Matter protesters who blamed the 1994 crime bill that he signed into law for America's mass incarceration — a law that Hillary advocated for and Bernie Sanders voted for.

This has become a consistent line of attack against the Clintons. In a scathing op-ed, Michelle Alexander, author of The New Jim Crow, suggested the 1994 law was a big contributor to mass incarceration. Historian Donna Murch echoed the sentiment. News reports even occasionally treat the claim — that the 1994 crime law was a big cause or the driver of mass incarceration — as fact.

But as journalist Kevin Drum noted in a blog post at Mother Jones, the 1994 law simply didn't have that much of an effect on prisons and jails: The black incarceration rate in particular continued a decade-plus-long climb after the law, but began a steady decline soon after.

The law's effect was small for one simple reason: States preside over the great bulk of the US justice system. So it's actually state policies that fueled mass incarceration — to the point that one could entirely exclude the federal prison system and America would still be the world's leader in incarceration.

This context is important not only because it demonstrates that the criminal justice policies Clinton supported weren't that significant to mass incarceration, but also because it helps show (as I'll get to later) that the Clinton White House and federal government were following a much broader tough-on-crime movement at a time when crime was historically high.

It's now easy to look back on that movement with scorn; I think mass incarceration is morally abhorrent, and the country should reverse it. But we're never going to be able to solve the problem if we don't look past the presidency.

Federal policy is not the cause of mass incarceration

Federal criminal justice policy, including much of the 1994 crime law, focuses almost entirely on the federal system, particularly federal prisons. It might be tempting to think of this system as huge — its name, federal prison, has a certain ring to it. But that's wrong.

In the US, federal prisons house only about 13 percent of the overall prison population. That is, to be sure, a significant number in such a big system. But it's relatively small in the grand scheme of things, as this chart from the Prison Policy Initiative shows:

One way to think about this is what would happen if a President Clinton or President Sanders used her or his pardon powers to their maximum potential — meaning, the president pardoned every single person in federal prison right now. That would push America's overall incarcerated population from about 2.2 million to 2 million.

That would be a hefty reduction. But it also wouldn't undo mass incarceration, and the US would still lead all but one country in incarceration — with an incarceration rate of about 629 per 100,000 people, only the tiny island country of Seychelles would come ahead.

So to really pull back mass incarceration, states will need to make changes. (And that will likely involve more than reforming drug laws: About 53 percent of state prisoners are in for violent crimes, and just 16 percent are in for drug offenses.)

The federal prison system is big — and the 1994 crime law, along with other tough-on-crime measures passed in the 1980s that expanded federal drug sentences in particular, made it bigger. But federal laws simply aren't the cause of mass incarceration.

The 1994 crime law included one big attempt to influence state policy — but it didn't really work

One caveat to all of this is that the federal government can try to influence state policy with funding incentives. For example, the Brennan Center for Justice, which supports undoing mass incarceration, proposed a potential federal law that would effectively give states money for plans to cut incarceration without increasing crime.

Indeed, the 1994 crime law, which the Clintons and Sanders supported, attempted to encourage states to adopt harsher criminal justice policies. Much of the law's criminal justice portions focused on federal policy, particularly increasing the length of federal prison sentences. But the law also provided funding for states to build prisons and, notably, adopt truth-in-sentencing laws that effectively increase prison sentences by requiring prisoners serve out at least 85 percent of their prison sentences without early release.

(The 1994 crime law was also bigger than prison sentencing policy, including a host of policies that liberals still support. It included the Violence Against Women Act, which helped crack down on domestic violence and rape; a 10-year ban on assault weapons; funding for firearm background checks; and grant programs for local and state police.)

But did the truth-in-sentencing incentives really influence state policies? Evaluations of the 1994 crime law suggest otherwise.

A 1998 report by the Government Accountability Office (GAO), for which federal investigators talked to state officials about whether the 1994 law influenced state policies, noted that just four states adopted truth-in-sentencing laws (TIS) solely as a response to the 1994 law:

At the time of our review, based upon determinations made by DOJ, 27 states had TIS laws that met the requirements for receiving federal TIS grants. For each of these 27 states, we contacted state officials to determine whether the availability of such grants was a factor in the respective state's decision to enact a TIS law. Based on the responses to our telephone survey, the states can be grouped into three categories—TIS grants not a factor (12 states), TIS grants a partial factor (11 states), and TIS grants a key factor (4 states).

Why did most states apparently not care for the 1994 law? Many state officials said that they were already interested in tough-on-crime measures before the federal law, GAO investigators found:

According to Ohio officials, the state passed its TIS law in 1995, which is later than the enactment date of the 1994 Crime Act. However, the officials told us the state law was based on a July 1993 report by the Ohio Sentencing Commission. Thus, according to the state officials, the availability of federal grants did not influence the state's decision to pass TIS legislation. Rather, according to Ohio officials, a widespread concern about early release of violent crime offenders was a major factor in the state's decision to pass TIS legislation.

Some state officials also argued that the funding incentives were too small to drive big policy changes. Vermont, for instance, said meeting the federal requirements for truth in sentencing would cost several million dollars but only result in about $80,000 in federal grants.

A more recent report, published by the National Institute of Justice in 2002, produced similar findings: "Overall, Federal TIS grants were associated with relatively few State TIS reforms. There was relatively little reform activity after the 1994 enactment of the Federal TIS grant program, as many States had already adopted some form of TIS by that time."

Another key point here: Truth-in-sentencing laws were only one way that federal and state governments embraced mass incarceration. They also flat-out increased prison sentences, adopted harsh mandatory minimum sentences, and encouraged police and prosecutors to be tougher on criminals. So even the impact the 1994 law had in states that embraced its funding was partial at best.

None of this is to exonerate the Clintons, Sanders, and the 1994 crime law they all supported for mass incarceration. They are all somewhat culpable — after all, the Clintons and Sanders backed a law that increased incarceration as one of its explicit goals.

But the reality is that the 1994 crime law did not create mass incarceration, and, indeed, mass incarceration was a result of much broader policies driven by a much broader nationwide movement.

Clinton and Sanders were supporting a much broader movement through the 1994 crime law

So what drove mass incarceration? Essentially, state policies — that increased prison sentences, expanded what counted as a crime worthy of jail and prison, and drove all the actors in the criminal justice system, particularly prosecutors, to push incredibly harsh punishments. Many of these policies predated the 1994 crime law.

Recently watched something with my kid my folks taped for me in Oct 94. Every campaign spot, from Ds and Rs, was a tough on crime ad. — Noah Rothman (@NoahCRothman) February 5, 2016

In the 1970s and '80s, crime rates were historically high. This created a political crisis in America, as the public, media, and politicians bought into the idea that punitive measures were necessary to combat the breakdown of society's moral fabric.

Take, for instance, the murder rate over the past several decades, which was unusually high from the 1970s through the early '90s:

The media went into a frenzy over these types of numbers, widely covering gang and gun violence, drug use among children, and the crack cocaine epidemic. This drove the public to demand that lawmakers do something about these problems. And policymakers responded with mass incarceration.

The idea was that more arrests, more prosecutions, and longer prison sentences would deter crime and drug use. Facing a crisis, US lawmakers pursued these policies with little concern for the costs — not just the financial burden, but the racial disparities and erosion of civil liberties they produced as well.

Criminal justice expert Mark Kleiman explained the mood at the time in a great piece for the Washington Monthly:

No one knew then that we'd seen the worst. All we knew is that the number of murders had more than doubled, that the total number of violent crimes had increased six-fold in the previous thirty years, that no reversal of trend seemed to be in sight, and that the street-level arms race financed by the crack trade had expanded the age range of killers and their victims down into adolescence. If you weren't seriously worried about crime in 1994, you just weren't paying attention.

Support for tough-on-crime laws was not exclusive to conservatives or Republicans. The 1994 crime law, for instance, got more votes from Democrats than Republicans in the House of Representatives. And then-Sen. Joe Biden spearheaded and supported many bipartisan tough-on-crime measures throughout the 1980s and '90s.

It's now easy to look back at these ideas with scorn. Criminal justice experts point out, for example, that incarceration reached the point of diminishing returns by the 1990s — there are only so many serious criminals out there, and by then the people getting put in prison weren't people who'd be committing crime after crime on the street. So mass incarceration was an ineffective way to fight crime.

The Clintons have also pulled back from the 1994 crime law. Bill Clinton conceded the law went too far. Hillary Clinton said of the 1980s and '90s anti-crime policies, "I think that a lot was done that went further than it needed to go and so now we are facing problems with mass incarceration."

But these policies were desperate responses to real crises at the time. State officials didn't need federal incentives to pursue mass incarceration. They just had to look at the country's problems with crime and drugs — and the media and public's demands that something be done — to feel like they had to act.

Recognizing all of this is crucial to understanding not just the context surrounding the 1994 law — which, again, was very flawed — but what America needs to do to reverse mass incarceration today.

Appreciate the limits of federal power — to fix mass incarceration

The focus on the 1994 crime law is problematic because it suggests that the president and Congress have a tremendous amount of power over the national criminal justice system. Experts, particularly John Pfaff at Fordham Law School, have long worried that this type of messaging from the media and politicians may cause people to expect too much from federal officials and too little from their local and state counterparts.

A recent example is when petitions asked President Barack Obama to pardon Steven Avery, who was depicted in Making a Murderer as perhaps wrongfully convicted. But Avery was convicted of a state crime, not a federal one, so Obama doesn't have the power to pardon him — a fact literally hundreds of thousands of petition signers seemed to miss.

This is a crucial distinction. For better or worse, the bulk of the criminal justice system is driven by state policies. And that means no president and no Congress can really put an end to mass incarceration — not without state cooperation. But if people don't get that, how can they know whom to put pressure on for serious criminal justice reform?

Watch: The school-to-prison pipeline, explained