THE FIRST time federal prosecutors in Arizona put a humanitarian volunteer on trial for the unpardonable offense of providing food, water and a change of clothes to a pair of Central American migrants, this spring, a deadlocked jury failed to convict. The second time, there was no such ambiguity — a new jury this month took barely two hours to produce an acquittal, meaning the prosecutors were all but laughed out of court.

The defendant, Scott Warren, a 37-year-old teacher, delivered a brief coda on the judicial ordeal he endured, in which he was charged with felonies that could have meant years in prison: “The government failed in its attempt to criminalize basic human kindness.”

Basic human kindness is not exactly the organizing principle of the Trump administration’s immigration policy, to put it mildly, but the conspicuous lack of it — in fact, the impulse to gratuitous cruelty — has repeatedly run afoul of the courts as well as the basic decency of most ordinary Americans. That was the lesson of last year’s systematic family separations, a festival of barbarism masquerading as a policy of deterrence. And that was the lesson of the misguided prosecutions of a good Samaritan in Arizona.

Mr. Warren is active in a group called No More Deaths, which is motivated by humanitarian and religious principles to assist desperate migrants who trek across the desert to reach the United States. Over the past couple of decades, thousands have died in an unforgiving landscape where temperatures can reach well above 100 degrees. The group leaves water and other supplies for migrants and offers medical care and clothing if needed. It is not engaged in human smuggling.

That distinction seems lost on some Border Patrol officers, who have surveilled and harassed the group and, in some instances, incredibly, poured out or destroyed water jugs left by volunteers for migrants. And it seems lost on prosecutors who have abetted the Trump administration’s crackdown on border activists and sought to make an example of Mr. Warren.

His “crime,” as described by Michael Bailey, the U.S. attorney for Arizona, was to drop by a small encampment known as the Barn, a gathering place for humanitarian workers just north of the Mexican border in southern Arizona, where he provided food, water and clothing for a pair of Central American migrants in January 2018. That fit the government’s puffed-up definition of “harboring” migrants, a felony that carries a stiff prison sentence. Sensibly, the jury didn’t buy it.

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