This just posted on nytimes.com:

The Obama administration has not always been completely clear about its immigration agenda, but it was forthright Tuesday when it challenged the pernicious Arizona law that allows the police to question the immigration status of people they detain for local violations. Only the federal government can set or enforce immigration policy, the government said in its lawsuit against the state, and “Arizona has crossed this constitutional line.”

Further on in the article the authors show exactly where the line is:

The current Supreme Court, fortunately, has not been as active in recognizing state power as was the Rehnquist court, but it is not always easy to predict its direction on a volatile issue like this one. Should the case reach the court, those justices with a constructionist bent might take note of Justice Hugo Black’s words from 1941, quoted by the Justice Department on Tuesday in support of its lawsuit: “The supremacy of the national power in the general field of foreign affairs, including power over immigration, naturalization and deportation, is made clear by the Constitution, was pointed out by authors of The Federalist in 1787, and has since been given continuous recognition by this Court.”

It’s nice to see the details for a change. Read the entire article here.