Justice Dept Files Suit Against Arizona.

[steelish]

Am I mistaken in understanding that the Arizona law is merely a tool which allows their police officers to actually enforce existing Federal laws?

You're exactly right. That is what the law is about. Not only doesn it allow Arizona officers to enforce an existing Federal Law, but it also points out (to the remainder of the U.S.) that the Federal government is dropping the ball.

(which is likely the REAL reason for the lawsuit)