It promises to be a bleak four years for liberals, who will spend it trying — and, most likely, failing — to defend health care, women’s rights, climate change action and other good things. But on one serious problem, continued progress is not only possible, it’s probable. That is reducing incarceration.

In an era of what seems like unprecedented polarization and rancor, this idea has bipartisan support. The Koch brothers and Black Lives Matter agree. The American Civil Liberties Union and the American Conservative Union Foundation agree. Bernie Sanders and Newt Gingrich agree.

Here’s what they agree on:

• The United States went overboard on mass incarceration in the 1980s and 1990s.

• This has ruined a lot of lives — of those incarcerated, yes, but also others among their families and communities.

• The evidence says that harsher sentences don’t prevent crime and may even lead to more crime.

• Jailing people is really, really expensive.