Democrats aren’t just responding to Trump. They are also facing increasing pressure from their left flank to abandon even a nominal commitment to immigration enforcement except in cases where such violations can be used like tax evasion against Al Capone — an excuse to lock up people who are guilty of other, more serious crimes.

Bernie Sanders, a democratic socialist, essentially was pummeled into submission for failing to support open borders in an interview with Vox. Rep. Joe Crowley (D-N.Y.), thought of as a potential future speaker of the House, is facing a progressive primary challenger who talks like this: “ICE is operating exactly as designed when it rips screaming children from parents. That’s exactly why we must abolish it.”

As The Atlantic’s Peter Beinart observed last year, a decade ago even liberals who supported an expansive immigration policy, including legal status for the bulk of the undocumented population, freely acknowledged the costs imposed by large-scale low-wage immigration, the challenges of assimilation in an era of reduced upward mobility, and the cultural tensions that can result.