Eric Holder v. Jan Brewer:

 The Justice Department filed suit Tuesday against Arizona, charging that the state's new immigration law is unconstitutional and requesting a preliminary injunction to stop the legislation from taking effect. The lawsuit says the law illegally intrudes on federal prerogatives, invoking as its main argument the legal doctrine of "preemption," which is based on the Constitution's supremacy clause and says that federal law trumps state statutes. The Justice Department argues that enforcing immigration laws is a federal responsibility. But the filing also asserts that the Arizona law would harm people's civil rights, leading to police harassment of U.S. citizens and foreigners.

The complaint is here (pdf). At 25 pages, it is two and a half times the length of the bill itself. One wonders if anyone in the Obama administration actually read this document given their infamous unwillingness to read the Arizona law.

Legal Times:

“In our constitutional system, the federal government has preeminent authority to regulate immigration matters. This authority derives from the United States Constitution and numerous acts of Congress,” reads the introduction   With the State Department joining as a plaintiff, the lawsuit also cites the president’s authority over foreign affairs. “Immigration law, policy, and enforcement priorities are affected by and have impacts on U.S. foreign policy, and are themselves the subject of diplomatic arrangements,” it says.   In a news release, Attorney General Eric Holder Jr. focused on two additional areas: the impact the law could have on immigrants’ willingness to cooperate with local police in criminal investigations, and the police resources that could be diverted from other investigations.

Republican Rep. Darrell Issa:

“For the better part of two decades, citizens in border states like Arizona, Texas and California have been told that illegal immigration enforcement is the responsibility of the federal government while their concerns about the safety of their families and communities have been largely brushed aside or met with inconsistent, under-resourced and ineffective responses from the federal government.  They now find themselves over-run by drug cartels, gangs and human trafficking.  The people who live under the constant threat of border violence have every right to be protected and have every right to defend themselves, their families and their communities. “For President Obama to stand in the way of a state which has taken action to stand-up for its citizens against this daily threat of violence and fear is disgraceful and a betrayal of his Constitutional obligation to protect our citizens.  Rather than spend time, energy, resources and money stopping a state from enforcing existing immigration laws, the Obama Administration should instead mobilize every resource available to stand with these states and families who live daily with the reality of violent crime along an unsecure border and suffer the consequences of the federal government’s failure.”

Perhaps it's a better legal argument than a political one, but the federal government does seem to be opening quite the can of worms to argue that a state-level attempt to do what the federal government claims is its sole responsibility is uncalled for while that same government is spending time and energy suing Arizona while it continues to not live up to its responsibility.