Supremacy Clause in the Constitution - Basis for Immigration Suit

Article VI, Clause 2 of the Constitution is being used as the basis for the Obama/Holder challenge to the Arizona immigration law. Item [2] of the ruling below gives the ground rules for the challenge.

The Supremacy Clause has been interpreted to come in effect only when the Federal Government has acted in a given field. In the case of Edgar v. Mite Corporation, 457 U.S. 624 (1982), the Supreme Court ruled that "A state statute is void to the extent that it actually conflicts with a valid Federal statute." In effect, this means that a State law will be found to violate the supremacy clause when either of the following two conditions (or both) exist:

[1] Compliance with both the Federal and State laws is impossible,

[2] "...state law stands as an obstacle to the accomplishment and execution of the full purposes and objectives of Congress..."

Read the Wikipedia analysis of the clause here.

As an aside, in reading this article, you would think that the Federal Government is all-powerful. However, they are only "Supreme" if their initial law is Constitutional and, according to the Constitution, their powers are limited to those specified, and those specifically granted to them by the States.