An arrest or search-and-seizure warrant must be signed by a judge who as a rule concurs that probable cause for prosecution, such as an indictment or sworn testimony or evidence, To be sure, a judge's signature may be no better than the competence of the Grand Jury that issues an indictment or the integrity of the police officers or prosecuting attorney. Well, that will be determined in a court of law, will it not?
A judge signing a warrant is a formality -- but not a formality for a local law-enforcement official such as a chief of police. Were I a judge I would be lenient on signing an arrest or seizure warrant. In a drug case that would be that activity looks like drug activity. A government bureaucrat on claiming that someone is an illegal alien? Probably not good enough.
What is a drug dealer doing wrong that an illegal immigrant isn't?