The US House of Representatives on Thursday passed a criminal justice reform bill, sending the most significant changes to the federal criminal justice system in decades to President Donald Trump’s desk.

The Senate previously overwhelmingly approved the legislation in an 87-12 vote.

The bill, called the First Step Act, makes modest changes to the federal system. It very slightly pulls back punitive mandatory minimum sentences by, for example, letting judges give lower sentences in some circumstances and relaxing a “three strikes” law to give 25 years instead of life in prison. It makes 2010 crack sentencing reforms, which eased crack sentences to bring them more in line with powder cocaine penalties, retroactive. It expands “good time credits” that well-behaved inmates can use to get out of prison a little earlier. It creates “earned time credits” that encourage inmates to take part in rehabilitative programs for an earlier release.

It doesn’t end the war on drugs or mass incarceration. It won’t stop police from locking up nonviolent drug offenders. It doesn’t legalize marijuana. It doesn’t even end mandatory minimums or reduce prison sentences across the board, and it in fact only tweaks both. As the First Step Act’s name suggests, its supporters consider it a first step.

The bill also only affects 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. In general, federal legislation can encourage municipalities and states to change their laws and systems, but ultimately, local and state lawmakers have the final word at the lower levels of government.

In total, the First Step Act will let a few thousand inmates — likely around 6,000 to 7,000 — out of prison early once it’s enacted, and slightly shorten prison sentences in the future.

As Stanford drug policy expert Keith Humphreys noted in the Washington Post, more than 1,700 people are released from prison every day already. So the bill in one sense equates to adding a few more days of typical releases to the year.

Even though Trump ran on a “tough on crime” platform in which he promised to support harsh prison sentences, the president has come to support the legislation — in large part thanks to the backing of key advisers, including his son-in-law Jared Kushner. He’s expected to sign the bill in the coming days.

For more on the bill, read Vox’s explainer.