The criminal justice reform bill that the Senate passed on Tuesday is the biggest change to the federal criminal justice system in decades. But it is also, despite headlines describing it as “sweeping” and an “overhaul,” a very modest bill.

It’s right there in the name: It’s called the First Step Act, acknowledging that it’s, well, a first step. The bill doesn’t end the war on drugs or mass incarceration. It won’t stop law enforcement from locking up nonviolent drug offenders. It doesn’t legalize marijuana. It doesn’t even end mandatory minimums or reduce prison sentences across the board, and it in fact only tweaks both.

This isn’t to take away from the legislation or suggest that it wasn’t worth doing. Thousands of federal prison inmates will benefit from the bill. But it’s important to put the bill in a broader context — to not oversell its impact, and to acknowledge there’s still a lot more room to make America’s federal criminal justice system less punitive.

To that end, there are two things about the First Step Act to keep in mind: First, the changes are really modest tweaks. Second, it only affects the federal criminal justice system, not the state and local systems that make up a great majority of America’s criminal justice framework.

The First Step Act’s changes are fairly modest

The First Step Act makes what I would characterize as meaningful tweaks to the federal criminal justice system. It very slightly pulls back punitive mandatory minimum sentences, by, for example, letting judges give lower sentences in some circumstances, and relaxing a “three strikes” law to give 25 years instead of life in prison. It makes 2010 crack sentencing reforms, which eased crack sentences to bring them more in line with powder cocaine penalties, retroactive. It expands “good time credits” that well-behaved inmates can use to get out of prison a little earlier. It creates “earned time credits” that encourage inmates to take part in rehabilitative programs for an earlier release.

In total, the bill will let a few thousand inmates — probably around 6,000 to 7,000 — out of prison early once it’s enacted, and slightly shorten prison sentences in the future. That may sound like a lot, but keep in mind the federal prison system currently holds nearly 181,000 people, and 2.1 million people are in prison or jail in America.

As Stanford drug policy expert Keith Humphreys noted in the Washington Post, more than 1,700 people are released from prison every day already — so the bill in one sense equates to adding a few more days of typical releases to the year.

It’s not nothing. To the extent that a bill like this needed to get by a Republican-controlled House, Senate, and White House, and get at least some Democratic approval to pass, it’s a solid compromise.

And given that America incarcerates the most people out of any country in the world, and that the research shows that mass incarceration is ineffective and even counterproductive for crime-fighting, it’s a positive step in the right direction.

But it doesn’t touch the primary drivers of mass incarceration in America.

The First Step Act only affects the federal criminal justice system

As a federal bill, the First Step Act only directly affects the federal criminal justice system. This is a reality of federalism in the US: While federal legislation can try to incentivize state laws and systems to move in a certain direction, the federal government ultimately only sets policy and laws at the federal level.

This is an important caveat for criminal justice reform, because the federal system is a small (but significant) part of the overall criminal justice system.

Consider the numbers: According to the US Bureau of Justice Statistics, 87 percent of US prison inmates are held in state facilities (and most state inmates are in for violent, not drug, crimes). That doesn’t even account for local jails, where hundreds of thousands of people are held on a typical day in America. Just look at this chart from the Prison Policy Initiative, which shows both local jails and state prisons far outpacing the number of people incarcerated in federal prisons:

One way to think about this is what would happen if President Donald Trump used his pardon powers to their maximum potential — meaning he pardoned every single person in federal prison right now. That would push down America’s overall incarcerated population from about 2.1 million to about 1.9 million.

That would be a hefty reduction. But it also wouldn’t undo mass incarceration, as the US would still lead all but one country in incarceration: With an incarceration rate of around 593 per 100,000 people, only the small nation of El Salvador would come out ahead — and America would still dwarf the incarceration rates of other developed nations like Canada (114 per 100,000), Germany (76 per 100,000), and Japan (41 per 100,000).

Similarly, almost all police work is done at the local and state level. There are about 18,000 law enforcement agencies in America, only a dozen or so of which are federal agencies.

The federal government could encourage municipalities and states to reform their justice systems — through, for example, grants incentivizing less incarceration. That’s something that criminal justice reformers have pushed for in recent years, like the Brennan Center for Justice’s Reverse Mass Incarceration Act, which would provide funds to simultaneously cut incarceration and crime.

But these incentive programs seem to only work if municipalities and states actually want the policies that they encourage. For example, studies found that the 1994 federal crime law, which encouraged more incarceration, only led a handful of states, at best, to actually change their laws. In fact, many states had already moved toward mass incarceration before the federal law.

Criminal justice reform, then, is going to fall largely to municipalities and states, and a bill that might slightly cut incarceration on the federal level isn’t going to have a very big effect. (To this end, many cities and states are actually way ahead of the federal government when it comes to criminal justice reform, with many passing the kinds of sentencing reforms that the federal system has struggled to enact.)

That’s not to downplay the work of criminal justice reformers who are trying to reduce the size and burden of what amounts to a fairly large prison system at the federal level. But to understand the bill, it’s important to put its full impact on mass incarceration in the broader national context.

For more on mass incarceration, read Vox’s explainer.

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