The Supreme Court debated four provisions of the Arizona immigration law, SB 1070. The sections of the law up for debate were 2(B), 3, 5(C) and 6. Section 2(B) requires Arizona law enforcement officers to make a “reasonable attempt,” “when practicable,” to ascertain the immigration status of any person whom an officer lawfully stops, detains, or arrests “where reasonable suspicion exists that the person is an alien and is unlawfully present in the United States.” Section 3 provides that an alien who willfully fails “to complete or carry an alien registration document” in violation of 8 U. S. C. §1304(e) or §1306(a) is guilty of a misdemeanor. Section 5(C) makes it a misdemeanor for an unauthorized alien who is unlawfully present in the United States “to knowingly apply for work, solicit work in a public place or perform work as an employee or independent contractor.” Section §6 authorizes Arizona law enforcement officers to arrest without a warrant any person whom the officer has probable cause to believe “has committed any public offense that makes the person removable from the United States.”
Some of the prevailing reasons that Arizona took the steps necessary to craft, debate and pass SB 1070 can be found on page six of the Majority Opinion of the Court: "Arizona bears many of the consequences of unlawful immigration. Hundreds of thousands of deportable aliens are apprehended in Arizona each year. Unauthorized aliens who remain in the State comprise, by one estimate, almost six percent of the population. And in the State’s most populous county, these aliens are reported to be responsible for a disproportionate share of serious crime (estimating that unauthorized aliens comprise 8.9% of the population and are responsible for 21.8% of the felonies in Maricopa County, which includes Phoenix). Statistics alone do not capture the full extent of Arizona’s concerns. Accounts in the record suggest there is an “epidemic of crime, safety risks, serious property damage, and environmental problems” associated with the influx of illegal migration across private land near the Mexican border. Phoenix is a major city of the United States, yet signs along an interstate highway 30 miles to the south warn the public to stay away. One reads, “DANGER—PUBLIC WARNING—TRAVEL NOT RECOMMENDED / Active Drug and Human Smuggling Area / Visitors May Encounter Armed Criminals and Smuggling Vehicles Traveling at High Rates of Speed”. The problems posed to the State by illegal immigration must not be underestimated.”
The foundation of the majority opinion's response lies in the Constitution's Supremacy Clause (Article 6, Paragraph 2): "This Constitution, and the Laws of the United States which shall be made in Pursuance thereof; and all Treaties made, or which shall be made, under the Authority of the United States, shall be the supreme Law of the Land; and the Judges in every State shall be bound thereby, any Thing in the Constitution or Laws of any state to the Contrary notwithstanding."
In short, the Justices in the majority used the Supremacy Clause as justification for striking sections 3, 5(c) and 6 from the Arizona law. They interpreted the Supremacy Clause as giving Congress the ability to imply specified powers from the States which, therefore, displaces state law altogether and that state law is preempted when it conflicts with federal law. Their reasoning is that the Arizona law attempted to preempt federal law on those duties reserved specifically for the federal government.
The dissenting Justices cited that the federal government is a "union of sovereign states." As a sovereign state, Arizona has the inherent power to exclude people from its territory and the power to exclude lies as a foundation to the state's sovereignty. The basis for their argument consisted in writings in from the Federalist papers, the Articles of Confederation and other articles of history. Justice Scalia argues that "before the adoption of the constitution of the United States" each state had the authority to prevent itself from being burdened by an influx of persons" and after the adoption of the Constitution, this right of the states was not stripped from them. To prevent the lax citizenship standards of one state from another state, the general government established a uniform rule of naturalization. This uniform rule was not to devolve the powers from the individual states but to strengthen the individual states rule regarding citizenship. The states had a sovereign interest in protecting their borders. It is an understood maxim of international law that "every sovereign nation has the power, as inherent in sovereignty and essential to self-preservation; to forbid the entrance of foreigners within its dominion…this is why there was no need to set forth control of immigration as one of the enumerated powers of Congress."
What remains unsaid in the Majority Opinion and what is explicitly stated in the dissenting opinions is expressed by Scalia, "It [Arizona law] applies to aliens who neither possess a privilege to be present under federal law nor have been removed pursuant to the Federal Government's inherent authority." The Majority implies that those who are not in the US legally are entitled to the same benefits and privileges as those in the country legally. Those in dissent understand that aliens are not entitled to the benefits and privileges as those legally present in the US.
With the underlying reasoning established, we can analyze each section under debate and what pro-enforcement advocates can do next.