As everyone knows, Arizona passed a law that says, among other things, state law enforcement will inquire with the feds about the status of suspected illegal aliens. The Obama administration says that this law upsets the entire federal immigration scheme and is unconstitutional. I’d be curious to know how, then, the Obama administration explains this passage in the U.S. code, which obviously contemplates state and local governments finding out about illegals and making inquires about them with the feds–indeed, forbids anyone from preventing this exchange of information from taking place:

Sec. 1373. Communication between government agencies and the Immigration and Naturalization Service
(a) In general Notwithstanding any other provision of Federal, State, or local law, a Federal, State, or local government entity or official may not prohibit, or in any way restrict, any government entity or official from sending to, or receiving from, the Immigration and Naturalization Service information regarding the citizenship or immigration status, lawful or unlawful, of any individual. (b) Additional authority of government entities Notwithstanding any other provision of Federal, State, or local law, no person or agency may prohibit, or in any way restrict, a Federal, State, or local government entity from doing any of the following with respect to information regarding the immigration status, lawful or unlawful, of any individual: (1) Sending such information to, or requesting or receiving such information from, the Immigration and Naturalization Service. (2) Maintaining such information. (3) Exchanging such information with any other Federal, State, or local government entity. (c) Obligation to respond to inquiries The Immigration and Naturalization Service shall respond to an inquiry by a Federal, State, or local government agency, seeking to verify or ascertain the citizenship or immigration status of any individual within the jurisdiction of the agency for any purpose authorized by law, by providing the requested verification or status information.

The brief in support of Arizona by state attorneys general is particularly good on this point:

… First, Congress has provided that the executive branch has no discretion regarding whether to answer an inquiry from a State regarding the immigration status of a person in custody. Under 8 U.S.C. § 1373(c), Federal immigration authorities “shall respond” to an inquiry from a State agency seeking to verify the citizenship or immigration status of any individual within that State’s jurisdiction. In fact, the U.S. “may not” prohibit or restrict a State from seeking information regarding the citizenship or immigration status of any individual. 8 U.S.C. § 1373(a). Likewise, Federal, State, and local entities are barred from preventing their officials from exchanging information with Federal immigration office. 8 U.S.C. § 1373(b). Again, Congress’s use of the word “shall” in § 1373(c) demonstrates that the executive branch lacks any discretion whether to answer these inquiries. Nor does the statute limit in any way the number of inquiries a State might make. Therefore, the executive branch’s discretionary allocation of resources cannot justify its preemption argument. Indeed, this very argument was rejected by the Ninth Circuit in Chicanos Por La Causa v. Napolitano, 558 F.3d 856, 866-867 (9th Cir. 2009) (holding that Arizona’s requirement to participate in E-Verify was not preempted because “while Congress made participation in E-Verify voluntary at the national level, that did not in and of itself indicate that Congress intended to prevent States from making participation mandatory”).
Second, Congress has stated that the Attorney General “shall” cooperate with the States to assure that information that would assist State law enforcement in arresting and detaining “an alien illegally present in the United States” under certain conditions is made available to such officials. 8 U.S.C. § 1252c(b). Congress’s use of the word “shall” indicates a mandatory, rather than discretionary, duty on part of the executive branch to assist State law enforcement in carrying out the State’s prerogative under 8 U.S.C. § 1252c(a). Because the Congress has not given the executive branch any discretion in determining whether to assist Arizona, its complaints about draining Federal resources cannot form the basis of a claim of preemption.
Finally, any claim that S.B. 1070 interferes with the Federal government’s allocation of resources must fail because Arizona does not, and cannot, place any obligation on the Federal government after an unlawful alien is reported. Under A.R.S. 11-1051(C), a law enforcement agency “shall” notify Federal immigration officials. Once that notification has been completed, it is ultimately up to the Federal government how to proceed. The Federal government could, for example, exercise its discretion by allowing the unlawful alien to remain in the United States in the interest of providing humanitarian relief. Or the Federal government could simply refuse to process any unlawful alien referred to them by Arizona officials, as suggested in May 2010 by the head of the Immigration and Customs Enforcement agency….