In response to this item, discussing the judgment calls that Chinese security forces make when asking for a foreigner's "papers," and what lessons their practice may hold for Arizona policemen planning to enforce the state's new immigration law, an American academic who asks not to be named sends this account:

A quick follow-up to the second emailer's comment that Chinese authorities are "looking for people with subversive ideas or tendencies, not people who are simply present illegally." This was not my experience in Tianjin, a large but less-known city near Beijing.

While I was visiting my wife (who was living in Tianjin continuously for a year), the police dropped by unannounced several times to spot check that everyone in the apartment had registered their passport at the local police station (required by law within 24 hours of arrival).

On one visit, I had registered, and on another, I hid in the bedroom. The process for registering took about 3 hours, and it was clear that the station bureaucrats were not used to doing it. So it seemed to be an individual tic of an aggressive police officer rather than a system-wide policy. But that just points up the problem of granting such wide authority under Chinese and Arizona law: when you make enforcement discretionary, you're ensuring that enforcement will be uneven, subjective, unpredictable, and thus open to abuse.

And now, from a reader in Texas:

Houston's local talk radio shows are now warning that all those Mexicans will now be fleeing AZ and movin' to Houston.

I wrote back to ask: Were the talk shows using this as a reason to oppose the Arizona law? Or instead to emulate it in Texas? The answer was what I expected (but it's worth being sure):

It was definitely made as an inspiration to follow it.

As a matter of jurisprudence, party politics, economics, inter-American relations, and social comity, this story is going to be unfolding for quite a long time.