The First Step Act, which passed with overwhelming support from Republicans and Democrats, takes modest steps to alter the federal criminal justice system and ease very punitive prison sentences at the federal level. It affects only the federal system — which, with about 181,000 imprisoned people, holds a small but significant fraction of the US jail and prison population of 2.1 million.
The law allows thousands of people to earn an earlier release from prison and could cut many more prison sentences in the future.