The administration has had a fit of honesty. They state in the complaint:

“…S.B. 1070’s mandatory enforcement scheme will conflict with and undermine the federal government’s careful balance of immigration enforcement priorities and objectives. ”

Here is evidence of their priorities and objectives: The sign warning Americans to not travel in southern Arizona

All the more evidenced since they haven’t said boo to Rhode Island, which has been identifying and reporting illegals found in the course of their lawful actions for years.