Governor Susana Martinez of New Mexico has taken some heat for an executive order regarding checking the immigration status of arrestees.  Columnist Ruben Navarette comes to her defense in this piece, distinguishing people arrested from those merely detained.  After comparing polar opposite approaches to immigration status, he writes,

Neither of these approaches makes sense. The better alternative is in the middle. The trigger for a state or local law enforcement agency questioning someone's immigration status should be an arrest, not a stop or a detention, as it is in Arizona.

That's good policing. And that's what Martinez is trying to encourage. For her, this isn't about cracking down on the undocumented to advance a political agenda.

"What I've done is purely a public safety issue," she said, "not an immigration issue."

A stop or detention requires only reasonable suspicion that criminal activity is afoot, under the 1968 decision in Terry v. Ohio (written by CJ Earl Warren).  An arrest requires probable cause to believe the person has committed a crime, and in most states a crime above the minor infraction level.