Outrageous consequences of this approach appear with dismal regularity. The latest was the arrest and 23-day detention of an American-born United States citizen because officers at one of many checkpoints in South Texas didn’t believe that the documents he showed were real. Francisco Erwin Galicia, 18, said he had lost 26 pounds at the overcrowded immigrant detention center, where men slept on the floor and were not allowed showers. Mr. Galicia was released only after The Dallas Morning News learned and told his story.

There are valid reasons Customs and Border Protection agents might have wanted to take a closer look at Mr. Galicia’s documents. His brother and another passenger in the car in which he was stopped were undocumented immigrants, as is his mother, who used a false name on his birth certificate. These are the sad realities of the lives of people who lack legal status in the United States.

But his detention was hardly an isolated mistake — hundreds of American citizens have now been detained on suspicion that they are living illegally in the United States, including a man held in custody for 1,273 days. Mr. Galicia had sufficient proof of American citizenship to rate a far speedier investigation.

The entire system of checkpoints, detention centers and immigration agents hunting for Hispanics — along with all the horror of children penned in disgusting conditions and a cascade of immigration policies that violate fundamental rights — perverts American values and traditions. It is a victory for the xenophobic and racist vision promoted by President Trump’s far-right adviser Stephen Miller and exploited by Mr. Trump from the day he announced his candidacy.

Among their latest sallies was a rule announced this month that would deny asylum to anyone who had failed to apply for — and be denied — protections in at least one country they passed through on their way north. That means Hondurans and Salvadorans would have to apply for asylum in Guatemala or Mexico before they could apply in the United States. Mexico has refused to go along with the scheme, but the White House said on Friday that Guatemala had agreed to a “safe third country” agreement, under which it would require migrants heading north to seek asylum there. Guatemala had balked at going along with the scheme until Mr. Trump threatened the country with tariffs, remittance fees and an unspecified “ban.”