Jerry Markon and Anne E. Kornblut
Washington Post 
April 29, 2010
Officials in the Obama administration are urging the extraordinary step of suing Arizona over its new immigration law, and the Justice Department is considering such an action to block the legislation from taking effect, government officials said Wednesday.
The Arizona law criminalizes illegal immigration by defining it as trespassing and empowers police to question anyone they have a “reasonable suspicion” is an illegal immigrant. President Obama and Attorney General Eric H. Holder Jr. have blasted the legislation, with Obama saying that it “threatened to undermine basic notions of fairness.”
“The president had strong words to say and the attorney general had strong words to say,” said one law enforcement official, who spoke on the condition of anonymity because no decision has been made. “Considering that it’s signed into law, and Arizona is doing a lot of pomp and circumstance, do you see a friendly way out of this?”
A key legal ground being considered, officials said, is the doctrine of “preemption” — arguing that the state’s law illegally intrudes on immigration enforcement, which is a federal responsibility.