Popularity makes no law invulnerable to invalidation. Americans accept judicial supervision of their democracy -- judicial review of popular but possibly unconstitutional statutes -- because they know that if the Constitution is truly to constitute the nation, it must trump some majority preferences. The Constitution, the Supreme Court has said, puts certain things "beyond the reach of majorities."
But Arizona's statute is not presumptively unconstitutional merely because it says that police officers are required to try to make "a reasonable attempt" to determine the status of a person "where reasonable suspicion exists" that the person is here illegally. The fact that the meaning of "reasonable" will not be obvious in many contexts does not make the law obviously too vague to stand. The Bill of Rights -- the Fourth Amendment -- proscribes "unreasonable searches and seizures." What "reasonable" means in practice is still being refined by case law -- as is that amendment's stipulation that no warrants shall be issued "but upon probable cause." There has also been careful case-by-case refinement of the familiar and indispensable concept of "reasonable suspicion."...
Probably 30 percent of Arizona's residents are Hispanics. Arizona police officers, like officers everywhere, have enough to do without being required to seek arrests by violating settled law with random stops of people who speak Spanish. In the practice of the complex and demanding craft of policing, good officers -- the vast majority -- routinely make nuanced judgments about when there is probable cause for acting on reasonable suspicions of illegality.
Arizona's law might give the nation information about whether judicious enforcement discourages illegality. If so, it is a worthwhile experiment in federalism.It's worth reading the whole thing.