Today, about 2.2 million Americans are behind bars. "The incarceration rate is about five times the rate of 1970 and our crime rate is the same as in 1970."

Our guest, John Pfaff of Fordham University is both a law professor and an economist. Author of "Locked In: The True Causes of Mass Incarceration—and How to Achieve Real Reform," he says state and local policies matter far more than changes in the federal system.

At about 700 inmates per 100,000 residents , the U.S. incarceration rate is five times higher than most western nations. Only North Korea and Iran have locked up a larger share of their population.

Growing bi-partisan support for criminal justice reform may bring changes. But Attorney General Jeff Sessions is going in the opposite direction. He's ordered federal prosecutors to pursue the strictest charges and sentences in criminal cases-- reversing Obama Administration policies.

The standard explanation for America's inmate population explosion is "three strikes and you're out" sentencing and other aspects of the federal government's war on drugs.

John Pfaff says that argument is far too simplistic. In this episode, we look at the key role played by state and local prosecutors. John argues that one key reform would be to focus on charging policies-- reigning in the almost unchecked power of many district attorneys.