The regulation of immigration is intertwined with the national government's exclusive conduct of foreign policy. "[I]nternational controversies of the gravest moment, sometimes even leading to war, may arise from real or imagined wrongs to another's subjects inflicted, or permitted, by a government." It is the national government, not the 50 individual States, that must prioritize the various national interests in such areas because "a single State" that inserts itself into immigration enforcement contrary to federal policies and objectives "can, at her pleasure, embroil us in disastrous quarrels with other nations."

In July, soon after the injunction was issued, the Ninth Circuit denied Arizona's request for expedited appeal [JURIST reports]. The preliminary injunction came at the request of the DOJ, which originally filed suit challenging the constitutionality of the law [JURIST report] in July. Judge Bolton of the district court issued the injunction against provisions of the law requiring the verification of the immigration status of people reasonably suspected of being illegal immigrants, authorizing the warrantless arrest of those police have probable cause to believe have committed an offense that could lead to deportation and requiring noncitizens to carry their registration papers with them at all times. The American Bar Association filed an amicus curiae brief [JURIST report] in support of the DOJ lawsuit, following the submission of another amicus curiae brief [JURIST report] filed by the American Civil Liberties Union.