Immigration and Customs Enforcement officers. (John Moore/Getty Images)

THE TRUMP administration’s failing campaign to bully so-called sanctuary states and cities by denying federal grants to police departments unless they offer unconditional cooperation to U.S. deportation agents is a study in the arrogance of power.

Nowhere did Congress impose such conditions on the public-safety funds it approved to help local law enforcement. Nowhere is it written that localities are obligated to hand over undocumented immigrants upon completion of their sentences to Immigration and Customs Enforcement officials — although in practice even most sanctuary jurisdictions do so in the case of inmates who have been convicted of serious violent crimes.

And in no way is it wise for Washington to compel states and cities to alienate immigrant communities, which is why so many jurisdictions and local law enforcement agencies draw the line at rendering inmates incarcerated for relatively minor crimes to federal agents.

On Thursday a three-judge panel of the U.S. Court of Appeals for the 7th Circuit in Chicago skewered the administration for trying to wield “the sword of federal funding to conscript state and local authorities to aid in federal civil immigration enforcement.” Its ongoing attempt to do so, the court said, is exactly the sort of executive overreach the nation’s founders intended to check through the separation of powers.

“If the Executive Branch can determine policy, and then use the power of the purse to mandate compliance with that policy by the state and local governments, all without the authorization or even acquiescence of elected legislators, that check against tyranny is forsaken,” wrote Judge Ilana Rovner.

As it happens, Ms. Rovner was appointed to the bench by a Republican president, Ronald Reagan, as were the other two judges who ruled against the administration: Daniel A. Manion (also Reagan) and William Bauer (Gerald Ford). They upheld an injunction issued last fall by yet another Reagan appointee, U.S. District Judge Harry Leinenweber, who was a GOP state lawmaker before he was named to the bench.

These are not liberals who believe in coddling undocumented immigrants. They’re conservatives who know what Ms. Rovner called “usurpation of power” when they see it. They were similarly clear-eyed in distinguishing what they called a “red herring” — the suggestion by Attorney General Jeff Sessions and others that sanctuary cities somehow impede immigration enforcement — from the reality that ICE, the main federal deportation agency, “can and does freely operate in ‘sanctuary’ localities.”

The administration’s campaign against sanctuary jurisdictions targets federal grants often used by police and other law enforcement agencies to purchase basic equipment, including vehicles. The amounts are often paltry. Chicago, which sued to unlock the funds withheld by the Justice Department, has applied for just $1.5 million in the grants at issue this year; the city’s annual budget is nearly $10 billion.

By contrast, the stakes are anything but trivial. By treating localities as well as Congress as irrelevant in its deportation crusade, the administration broadcasts its contempt not only for immigrant communities but also for the rule of law.