It is not just the current cruelty which should frighten us. The border separations are of course immoral and unconscionable. Children are ripped from the arms of their mothers; they wail for Papa without answer; they are caged. Even when the immediate suffering of the 2,000 already taken has passed, many will be affected for life by the trauma. For some, the divisions will prove permanent. Parents are being deported without their children. Last month, a father killed himself after separation from his family. Yet as the human cost becomes starker, the pace of separations has increased.

Amnesty International argues that these acts deliberately inflict such mental suffering that they constitute torture – inflicted not just on adults facing harsh choices, but also children who cannot make choices at all. The president of the American Academy of Pediatrics rightly calls it child abuse. It demonstrates Donald Trump’s willingness to wield his power in the most brutal and intrusive ways and to dehumanise the victims, fostering the “us and them” culture in which he thrives. Its inhumanity is matched by its mendaciousness. It is another step along America’s alarming authoritarian path.

The administration has claimed there is no policy of separation. Mr Trump blames the Democrats. But these horrors result from the “zero tolerance” policy he introduced. Asked specifically about the cost to families, key aides portray separation as a deterrent. These mixed signals reflect the administration’s divisions, but also its ability to confuse opponents and throw them off balance. In truth, toddlers are being instrumentalised to persuade parents to stay away, to attempt to force harsh immigration reforms through Congress – and most of all to send a message to the base: not a dog whistle, but a klaxon.

Mr Trump has prospered not by appealing to the better angels of the country’s nature, but by feeding its demons. America is a nation of immigrants – whatever the administration may say – but people of colour have too often been treated as less than human, incapable of the same feelings and undeserving of the same rights; including that of family life. Slaves saw their children sold to other owners; Native Americans were snatched from their parents and placed in institutions. The Chinese Exclusion Act splintered families. Laura Bush drew a comparison with the mass internment of Japanese Americans, though George Takei, held as a five-year-old, writes that “even then, they didn’t separate children”.

Some hope that this is Mr Trump’s “Katrina moment”; that he has fatally misread the mood of the nation. Even prominent evangelical leaders have denounced the policy as antithetical to their family values. Yet Mr Trump retorts that illegal immigration “infests” the country. Advisers like speechwriter Stephen Miller believe that such controversies ultimately plays in his favour with voters.

It is vastly less helpful to many Republicans facing the midterms. But since they long ago threw in their lot with the president, the rhetorical backlash has yet to be matched by action. Mr Trump is using children as political hostages to force through harsh immigration reforms. Legislators must not be strong-armed into backing either of the Republican immigration reform packages – one punitive, the other far worse – the House of Representatives is likely to vote on this week.

The effects will be felt not only at home, but further away, as populist politicians draw inspiration and confidence. Virulent nativism is on the rise; Italy’s far-right interior minister Matteo Salvini has called for a census of the Roma community and expulsion of all non-Italian Roma. Democracy and a decent society are always works in progress, perpetuated and shored up by daily acts of commitment.

Historian Timothy Snyder reminds us that “the system does not in fact defend itself, it depends upon ethics and conventions, and … these have to be named, defended, and exemplified”. The GOP’s hunt for a face-saving compromise is on. But Republicans should not just condemn but outright oppose these shocking separations, and the attempt to use them as leverage. If they fail to do so, it falls to ordinary Americans to change their minds by uniting against this policy of hate.