A cell inside a federal prison in Coleman, Fla. (Nikki Kahn/The Washington Post)

The bipartisan congressional effort to reform federal criminal penalties has stalled, with little prospect of progress until autumn at the earliest. If you fear that Congress’ inaction could undermine the nation’s recent progress toward reversing mass incarceration, it may be helpful to reflect upon an underappreciated fact about American criminal justice: The number of people in prison has little to do with what happens in Washington.

In some policy areas, including health care, military affairs and the economy, the most consequential political decisions are made in the nation’s capital. But in the criminal justice system, states, cities and counties are the central players. For every federal law enforcement agent, about a half-dozen state highway patrol officers, county sheriffs and city police patrol the streets. Similarly, less than one-seventh of the country’s prison inmates are in federal facilities.

Because the federal prison system is so small, even dramatic congressional reforms in federal criminal penalties would have only a modest impact on the level of incarceration in the United States. Democratic presidential candidate Bernie Sanders was thus making an empty promise when he pledged to reduce the number of prisoners in the United States below that of China: Not even granting presidential pardons to every single federal prisoner would achieve this goal.

In addition to being small, the federal system also has an unrepresentative inmate population. Politicians, activists and major media outlets have pointed to federal prison statistics to argue that most people behind bars are nonviolent drug offenders. But such characterizations are misleading, because in the far larger state prison system, most offenders have violent convictions and less than 1 in 6 is serving time for a drug offense. Making a sizable dent in mass incarceration thus requires the shortening of sentences for violent crimes, a policy which currently has few defenders among elected officials or the public.

None of this is to say that Congress shouldn’t do its best to make the federal criminal code more fair, transparent and sensible. But whether the denizens of Capitol Hill succeed or fail in that quest, the path to reducing mass incarceration actually runs through all 50 state capitals.

Keith Humphreys is a professor of psychiatry at Stanford University.