Immigration, Foreign Affairs and the Constitution
Many "progressive" opponents of the Arizona immigration law are arguing that the law is unconstitutional because foreign affairs is exclusively the province of the federal government.
That foreign affairs is exclusively the province of the federal government is commonly asserted. But it is a myth – at least if one respects the Constitution’s text and original understanding.
First, the Constitution gives the federal government supreme authority over foreign policy. Congress and the President can pre-empt an issue by exercising one or more of their enumerated powers. If Congress dislikes a state action in that realm, Congress can pass a law overriding it.
If, however, Congress has not acted or acted incompletely, the states have certain reserved powers to act on their own. In other words, the Constitution acknowledges concurrent, although subordinate, state authority over foreign affairs – including immigration.
How do we know this? From both the constitutional text and from the record left by those who debated and ratified the Constitution.