Q&A: Arizona's illegal immigration law at Supreme Court
The US Supreme Court will hear arguments on Wednesday about the constitutionality of the state of Arizona's strict anti-illegal immigration law.
The closely watched case could determine whether America's 50 states and countless other jurisdictions are free to enact their own harsh laws, or whether the framework of federal immigration laws - widely viewed as inadequate - remains the last word on the issue.
What does the law do?
In April 2010, the Republican-led Arizona legislature approved a measure known as the Support Our Law Enforcement and Safe Neighborhoods Act, or SB1070 for its designation number in the state senate.
State lawmakers said Arizona, which shares a 370-mile (595km) border with Mexico, unfairly bears the brunt of Washington's inaction on illegal immigration, forcing them to act.
The law's stated goal is "attrition through enforcement" of illegal aliens living in Arizona.
Among other provisions, the law requires Arizona police to verify the immigration status of people they have detained for another reason if officers have a "reasonable suspicion" the person is in the US illegally.
It gives Arizona police the power to arrest a person without a warrant if they have "probable cause" to believe the person has committed a deportable offence.
It makes it a state crime not to complete or carry an alien registration document - this was already a federal civil violation. And it makes it a misdemeanour crime for an undocumented immigrant to apply for a job, to solicit work in a public place, or to work in the state.
Opposition to the bill was vigorous and broad, both within and outside the state. Opponents, especially Hispanic groups, said it would lead to the racial profiling of Hispanics and the persecution of legal immigrants.
What is its current status?
The federal government challenged the law immediately, and a lower federal court halted enforcement of the relevant parts of the law.
The law made its way through the federal court system, and in December, the Supreme Court agreed to hear the case.
Five states - Alabama, Georgia, Indiana, South Carolina and Utah - have adopted variations on Arizona's law. Parts of those laws are also on hold pending the outcome of the Supreme Court case.
What is the basis of the federal government's argument?
The key word for the federal government's case is "pre-empt" - as in, federal law pre-empts the Arizona law.
The Obama administration argues immigration law and policy are the exclusive remit of the federal government. It says states are forbidden to set their own immigration policy.
It argues that since immigration policy involves foreign policy decisions, it is the federal government, not the states, that has legal and constitutional responsibility over the treatment of aliens on US soil.
The federal government says the US already has a robust statutory and legal framework in place for handling immigration, however lacking it may be in addressing illegal migrants.
With SB1070, the Obama administration argues, Arizona imposes its own judgement on the "sensitive subjects" of immigration policy, the treatment of illegal immigrants, and international relations.
"For each state, and each locality, to set its own immigration policy in that fashion would wholly subvert Congress's goal: a single, national approach," the administration wrote in its brief.
The administration argues that the Arizona law conflicts with federal immigration policy by criminalising an act (being in the US without documentation) that the federal government treats as a civil violation.
It also objects to the law giving county prosecutors authority to charge undocumented immigrants with a crime even though federal prosecutors may have elected not to charge them (perhaps because they are seeking witness co-operation or for other reasons).
And the administration says the law requires local police to enforce federal law without regard to Washington's enforcement priorities.
How did Arizona respond?
The state of Arizona contends its law neither creates a conflict with federal laws nor imposes a separate immigration policy, but merely adds state resources to the enforcement of federal rules.
In the state's brief, it argues the immigration law is no different from situations where both federal and state law enforce the same federal standard for damages in civil suits.
The state argues Congress has already provided legal mechanisms for co-operation between state and federal authorities on immigration enforcement, and that its law merely extends those.
And it says state and local law enforcement already have inherent authority to investigate and prosecute violations of federal law.
The court will hear arguments beginning at 10am on Wednesday. Justice Elena Kagan, who worked for the Obama administration before she joined the court, will not be participating.
Arguing for the Obama administration is Solicitor General Donald Verrilli Jr, a former White House and justice department lawyer who has argued several cases before the Supreme Court.
Arguing for Arizona is Paul Clement, former solicitor general under President George W Bush.
Mr Clement is very well regarded in the Washington legal community and is highly experienced in Supreme Court arguments.
And he is the go-to man for American conservatives seeking a skilled advocate in the high court. Last month, he argued the Supreme Court should overturn President Barack Obama's signature healthcare law.
The two sides filed written briefs with the court this winter and spring. Whatever show of legal rhetoric and questioning comes on Wednesday, Supreme Court analysts say the Supreme Court justices often make up their minds ahead of time.
The court is not expected to issue its decision until the summer.