A Pennsylvania federal judge has taken the unusual step of urging an investigation into Philadelphia District Attorney Larry Krasner’s office over its handling of a man’s yearslong attempt to overturn a murder conviction. The development stands out because the court’s concern is not limited to the integrity of the conviction itself; it extends to whether prosecutors or officials in a major urban DA’s office may have engaged in conduct warranting criminal scrutiny.

That distinction matters.

A federal judge on July 2 temporarily blocked Philadelphia from enforcing a city measure aimed at federal immigration operations, preventing the city from requiring federal officers to go unmasked, display visible identification, and use marked vehicles during enforcement activity. The ruling is an early but important development in a fast-evolving conflict between local efforts to regulate immigration tactics and the federal government’s claim to operational control over its officers.

At the center of the dispute is a familiar constitutional fault line: whether a municipality can impose rules that affect how federal officers carry out federal law.