How can police in Arizona enforce the newly passed law requiring them to ask anyone they suspect of being an illegal immigrant for proof of citizenship?

I don’t mean this as a moral or ethical question, although 52-year-veteran Pima County Sherriff [sic], Clarence Dupnik, calls the law “disgusting” and says that it is “unwise” and a “national embarrassment”, and Phoenix Mayor Phil Gordon disclaims the bill as unrepresentative of and “humiliating” for his state’s population.

What I mean is simply this: will all US citizens in Arizona now routinely be required to carry passports, or birth certificates? And if not, what happens when citizens are stopped by suspicious police who think they may be undocumented migrants?

Coverage has rightly emphasized that the law, while claiming to be aimed at supporting detention of undocumented migrants, actually creates new burdens for those immigrants who are in the US legally. Legal immigrants now must carry their papers with them at all times or risk new penalties.

But the requirement to stop anyone “reasonably” suspected of being in the US without legal permission implies more: it will almost inevitably lead to native-born citizens of Hispanic heritage being stopped and asked to produce documents proving they are in the country legally as well. The only way for a native-born citizen to do so would be to produce a birth certificate or passport.