As President Trump steps back from the ledge on a mostly (though not entirely) self-inflicted political crisis at the border, liberals are shifting targets from migrant children being separated from their parents to families being detained at all.

Such comments are coming from progressives and activists, of course, not mainstream Democratic politicians. But even the Senate Democrats' legislation to address family separation would have severely undercut enforcement actions against undocumented parents with children within 100 miles of the border — and could plausibly be read to lead to more absurd outcomes.

Over the last few years, Democrats have with little fanfare moved dramatically to the left on immigration. This fact, combined with tepid opposition from the Republican governing class, contributed to Trump's rise. Trump's presidency has in turn further radicalized the Democrats on this issue.

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.

One of the liberals Beinart quotes allowing that he was bothered by seeing Mexican flags waved at pro-immigration protests and interacting with mechanics who could not speak English was Barack Obama. Obama, like George W. Bush in the final years of his second term, came into office believing that the best way to build support for legalizing illegal immigrants via "comprehensive immigration reform" was to establish some credibility on enforcement — something that had been sorely lacking since the 1986 amnesty signed into law by Ronald Reagan.

Obama's "deporter in chief" reputation was exaggerated by supporters and detractors alike. Nevertheless, he was comparatively strict. By 2012, however, it was evident that his enforcement initiatives were not going far enough for Republicans and went too far for progressive and immigrant activists. He then shifted gears.

The rest of the party is shifting further still. Where previous generations of liberals might have been worried about low-wage immigrants, legal or illegal, competing with similarly situated Americans, the dominant concern among contemporary progressives is the fact that immigrants are disproportionately people of color and thus any restrictions or enforcement will have a disparate impact on racial minorities.

Trump's frequent use of dehumanizing words and phrases when discussing immigration, plus his overall racial baggage, reinforces the growing liberal conviction that resisting immigration enforcement is the civil rights struggle of our time. Defending the indefensible on family separation has deepened the divide, but Democrats are gradually moving toward a position that is equally impractical unless you regard regulating immigration as illegitimate.

Many libertarians, a growing number of liberals, and even a few influential conservatives — think of the old Wall Street Journal editorials calling for open borders — do sincerely hold that belief. Democrats are in the main moving in that direction as a reaction to Trump rather than through reasoned debate.

But even many of the more sophisticated advocates for minimal immigration enforcement fail to reckon with the counterarguments: that there are costs to specific Americans even if there are (sometimes overstated) aggregate economic benefits; that those Americans are themselves disproportionately black and Latino; that the victims of MS-13 are frequently Hispanic; that upward mobility isn't what it used to be; that unregulated immigration does not seem to be having a liberalizing effect either here or in other Western countries and is in fact coinciding with at least a partial resurgence of white racism.

Instead we are having an immigration debate that pits the specific and cruel against the well-intentioned but overly abstract, exaggerated fears against happy talk that ignores inconvenient truths. It's no way to run a country, and certainly not a nation of immigrants.