Later this month, Barack Obama will become the first president in at least 40 years to leave the office with a smaller federal prison system than he started with. In 2015, the total incarceration rate — including state prisons, federal prisons and local jails — fell to 670 inmates per 100,000 U.S. residents.

That is the lowest it has been since around 1998, according to the latest report from the Bureau of Justice Statistics. The incarceration rate peaked in 2007 and 2008, at 760 inmates per 100,000. But since 2008 that rate has fallen every single year for seven years. The U.S. hasn't seen such a continued decline in incarceration since at least the 1960s.

As Stanford's Keith Humphreys explained on Wonkblog last week, much of the decline in the prison population is due to reforms happening at the state, rather than the federal, level. While federal reforms have largely been stalled in Congress, Obama's late-term clemency effort has cut short prisoners' sentences at a record pace among presidents.

The violent crime rate, meanwhile, also fell over the same period. In 2007, there were about 472 cases of rape, murder, robbery or aggravated assault for every 100,000 U.S. residents. By 2015, that number fell to 373 violent crimes per 100,000 people, a drop of about 20 percent.

In 2015, the states with the biggest drops in their incarcerated population also saw the biggest decreases in crime, according to the Pew Charitable Trusts.

Incarceration could be falling in those states simply because people are committing fewer crimes. But some researchers and criminal justice reformers believe the concomitant drop in incarceration and crime rates supports what they have been saying for years: There's little-to-no relationship between crime and incarceration. Shrinking the prison population isn't likely to have much of an impact on the crime rate in either direction, they say.

Part of this is because many of the people currently behind bars are low-level offenders, according to a recent Brennan Center for Justice report. Hundreds of thousands of people are behind bars for minor crimes like drug possession or burglary, and for them incarceration alternatives like probation, drug treatment or community service would be more effective, the Brennan Center concluded.

Many thousands more are serving unnecessarily long sentences for violent crimes, the researchers said. After a certain point, lengthy prison sentences don't have much more of a deterrent effect than shorter ones.

The latest report from the Bureau of Justice Statistics also underscored the extent to which the war on drugs is a significant driver of incarceration trends. About 1 in 5 inmates in state and federal prisons are serving time for a drug-related offense.


Drug crime makes up an even larger share of the federal judiciary's workload, as outlined in Supreme Court Chief Justice John Roberts's 2016 year-end report. Drug cases accounted for nearly a third of the federal criminal caseload at the district court level in 2016, roughly on par with prior years.

Still, the latest federal statistics show that America's decades-long trend toward mass incarceration has reversed direction during the Obama years. Given that much of this change is happening at the state level, it's a good bet that the trend will continue over the next four.

However, Trump has made a name for himself in part by adopting the "tough on crime" rhetoric of decades past. He also has exaggerated crime rates — he suggested this week that Chicago had an all-time record number of murders last year, though were more in the mid-90s — suggesting a personal interest in law and order issues. Whether he will translate any of that tough talk into concrete policy remains an open question.

More from Wonkblog:

Poor white kids are less likely to go to prison than rich black kids

There's been a big decline in the black incarceration rate, and almost nobody's paying attention

The states that spend more money on prisoners than college students