Keith Humphreys/The Washington Post (Keith Humphreys/Keith Humphreys/The Washington Post)

The recently enacted First Step Act reduces criminal sentences and promotes rehabilitative programs within the federal justice system. Combined with earlier reforms implemented during the Obama administration, the law should return the federal imprisonment rate back to what it was a generation ago. But that would still leave the federal prison system with about seven times as many inmates as it had in 1980. Could the United States ever return to a federal prison population that small, or would that unleash a horrific crime wave?

Questions about how big or small the federal prison system should be are part of the ongoing debate about mass incarceration. But they also have a unique dimension because even though the Constitution assigns most law enforcement powers to states, the federal role in prosecution and incarceration expanded in recent decades (e.g., to include many white-collar crimes, carjacking, DVD piracy, street-corner drug dealing). As a result, the federal prison system went from accounting for only 7.4 percent of all imprisonment in 1980 to 12.6 percent of all imprisonment in 2016. Even a decade before the federal prison system reached its peak size, a bipartisan American Bar Association task force argued that the expansion of federal law enforcement and corrections were “inconsistent with the traditional notion that prevention of crime and law enforcement in this country are basically state functions.”

Sometimes it is helpful in public policy to ask questions about first principles: Why should the federal government ever imprison anyone at all? A common fear — which some opponents of the First Step Act stoked — is that the United States would be overwhelmed with violent crime if not for federal law enforcement and incarceration. In reality, virtually every murder, rape, assault and battery is charged under state law and results in imprisonment at the state or local level. The federal prison system holds only 1.8 percent of U.S. inmates serving time for violent crimes.

Federal law enforcement and imprisonment thus do not serve as the nation’s primary bulwark against violence. But they are important in three defined contexts.

Combating state and local corruption. I grew up in West Virginia near a small city that was legendarily corrupt, from speed traps to sweetheart contracts to rigged elections. The graft went on for years until federal agents came in one shocking day and arrested the mayor, police chief, city attorney, and some city council and state officials who were in on the gravy train. When lower levels of government become completely bent, they lose the ability to self-correct, leaving federal intervention as the only solution. It is no accident Al Capone ended up in a federal prison (Alcatraz) because of a federal tax evasion charge rather than anything the Chicago cops on his payroll did to bring him to justice.

Battling criminal organizations that overwhelm state and local law enforcement. In its heyday, the Ku Klux Klan was powerful enough in many states to murder local officials that opposed it and terrorize any potential witnesses into silence. The advent of federal investigations, witness protection and incarceration under Secret Service Chief Hiram Whitley in the 1870s was critical for blunting the KKK’s power. Criminals that operate across state and, even more so, national borders including some human trafficking organizations, far-flung drug smuggling operations, gunrunning gangs, immigrant-smuggling “coyotes”, offshore money laundering operations and Internet child pornography rings are hard for state and local law enforcement to bring to heel due to jurisdictional issues and resource constraints. The power of federal law enforcement backed with the threat of federal imprisonment is essential in many such cases.

Punishing crimes specifically against the federal government. A small number of crimes are truly direct assaults on federal government, to which only it has the authority to respond. Counterfeiting currency, mail robbery and federal tax evasion are obvious examples. Treason, rigging federal elections and attempting to bribe members of Congress are others.

All of the above types of crimes are destructive, and those who commit them and are sent to federal prison do not deserve our sympathy. But it is implausible that the number of and deserved sentence length for such offenses are seven times greater than they were before the federal prison population exploded. That reality, combined with the fact that the generational cutback in the size of the federal prison system has caused no evident problems, suggest the First Step Act should be considered just that — a first step. The extremely broad coalition that supported the First Step Act can reasonably aim higher in its next round of proposed reform, returning the federal prison system to its traditional role as an important — but small — part of the U.S. correctional system.