Ha! What a great pissing match.
Personally, I don't care what Arizona does. It's their state to govern as they see fit, and if Obama doesn't like it, too bad. It's called the 10th Amendment, part of the Constitution he swore to uphold.
"The powers not delegated to the United States by the Constitution, nor prohibited by it to the States, are reserved to the States respectively, or to the people."