Judge Susan Bolton bought the Justice Department's preemption argument — i.e., the claim that the federal government has broad and exclusive authority to regulate immigration, and therefore that any state measure that is inconsistent with federal law is invalid.
The Arizona law is completely consistent with federal law. The judge, however, twisted to concept of federal law into federal enforcement practices (or, as it happens, lack thereof).
In effect, the court is saying that if the feds refuse to enforce the law the states can't do it either because doing so would transgress the federal policy of non-enforcement ... which is nuts.
This appears to be a classic case of a liberal judge, appointed by President Bill Clinton, bowing to the wishes of an even more liberal administration in Washington.
Did Judge Bolton make the ruling strictly on her own or did she get instructions (orders) from Eric Holder or someone else in the administration?