	Introduction

On June 25, 2012, the Supreme Court issued its much-anticipated decision in Arizona v. United States , ruling that some aspects of an Arizona statute intended to deter unlawfully present aliens from remaining in the state were preempted by federal law, but also holding that Arizona police were not facially preempted from running immigration status checks on persons stopped for state or local offenses. In reaching these conclusions, the Supreme Court made clear that opportunities for states to take independent action in the field of immigration enforcement are more constrained than some had previously believed. In recent years, several state and local governments have adopted measures intended to deter the presence of unauthorized aliens within their jurisdiction. An Arizona measure enacted in 2010, commonly referred to as S.B. 1070, arguably represents the vanguard of recent attempts to test the legal limits of greater state involvement in immigration enforcement. Before S.B. 1070, as amended, was scheduled to go into effect, the Department of Justice (DOJ) brought suit in federal district court seeking to preliminarily enjoin many (but not all) of the provisions of the Arizona measure, arguing that they were likely preempted by federal immigration law and therefore unenforceable under the Supremacy Clause. The district court granted the DOJ's motion to preliminarily enjoin four of the Arizona law's provisions (though it did not enjoin all the provisions of S.B. The Court's Decision in Arizona

Arguments at the Supreme Court centered on four major provisions of the Arizona statute, which can be divided into two categories: (1) those provisions seeking to bolster direct enforcement of federal immigration law by Arizona law enforcement, including through the identification and apprehension of unlawfully present aliens; and (2) those provisions that criminalize conduct which may facilitate the presence of unauthorized aliens within the state. The eight Justices who decided the case (Justice Kagan had recused herself) were asked only to consider whether the four enjoined provisions of S.B. Nor did it consider other constitutional challenges to the validity of the Arizona law, including claims that enforcement of S.B. 1070 would lead to impermissible racial profiling. 1070, which imposed criminal penalties upon unauthorized aliens who seek or obtain employment within Arizona. 1070, which authorized the warrantless arrest of aliens who have committed certain criminal offenses that constitute grounds for removal under federal law, is facially preempted. Immigration Status Determinations by State Police

Finally, the sitting Justices unanimously agreed that federal immigration law does not facially preempt Section 2(b) of S.B. 1070, which required Arizona police, whenever practicable, to investigate the immigration status of persons reasonably suspected of being unlawfully present when such persons are stopped, detained, or arrested pursuant to the enforcement of state or local law. 1070 were facially preempted by federal immigration law, and suggesting that a fourth provision could be susceptible to as-applied challenges, the Supreme Court clarified that the opportunities for states to take independent action in the field of immigration enforcement are more constrained than some had previously believed. Further, while the Court found that measures requiring or authorizing immigration status checks by state and local police are not facially preempted, the Court's decision suggests that such measures could be vulnerable to as-applied challenges, particularly if these status checks unreasonably prolong the detention of persons in state or local custody. However, the court enjoined the enforcement of the provision of S.B. 1070 was not facially preempted. In ruling that three provisions of Arizona's S.B.
On June 25, 2012, the Supreme Court issued its much-anticipated decision in Arizona v. United States, ruling that some aspects of an Arizona statute intended to deter unlawfully present aliens from remaining in the state were preempted by federal law, but also holding that Arizona police were not facially preempted from running immigration status checks on persons stopped for state or local offenses. In reaching these conclusions, the Supreme Court made clear that opportunities for states to take independent action in the field of immigration enforcement are more constrained than some had previously believed.
In recent years, several states and localities have adopted measures intended to deter the presence of unauthorized aliens within their jurisdiction. An Arizona measure enacted in 2010, commonly referred to as S.B. 1070, arguably represents the vanguard of these attempts to test the legal limits of greater state involvement in immigration enforcement. The major provisions of S.B. 1070 can be divided into two categories: (1) those provisions seeking to bolster direct enforcement of federal immigration law by Arizona law enforcement, including through the identification and apprehension of unlawfully present aliens; and (2) those provisions that criminalize conduct which may facilitate the presence of unauthorized aliens within the state.
Before S.B. 1070 was scheduled to go into effect, the Department of Justice (DOJ) brought suit to preliminarily enjoin many (but not all) of S.B. 1070's provisions, arguing that they were likely preempted by federal immigration law and therefore unenforceable under the Supremacy Clause. The district court granted the DOJ's motion to preliminarily enjoin four of the Arizona law's provisions, and the injunction was upheld by the U.S. Court of Appeals for the Ninth Circuit. The Supreme Court thereafter granted certiorari to review the case.
The eight Justices who decided the case (Justice Kagan recused herself) were asked only to consider whether the four enjoined provisions of S.B. 1070 were facially preempted by federal law. They did not consider other constitutional challenges to the validity of the Arizona law, including claims that enforcement of S.B. 1070 could lead to impermissible racial profiling. A majority of the Court found that the Arizona measure's criminal sanctions for alien registration violations and upon unauthorized aliens who seek employment in the state were preempted by federal law. The Court also ruled invalid a provision authorizing the warrantless arrest of aliens who have criminal offenses that constitute grounds for removal under federal immigration law. However, the sitting Justices unanimously agreed that federal law did not facially preempt a provision which requires Arizona police whenever practicable, to investigate the immigration status of persons reasonably suspected of being unlawfully present when such persons are stopped, detained, or arrested pursuant to the enforcement of state or local law—at least so long as the investigation does not extend these persons' detention by state or local law enforcement.
In ruling that three provisions of S.B. 1070 were facially preempted, and suggesting that a fourth provision could be susceptible to as-applied challenges, the Court clarified that opportunities for independent state action in the field of immigration enforcement are limited. In particular, the Court's decision would suggest that mirroring federal law when imposing criminal penalties upon conduct that could facilitate the presence of unauthorized aliens within a jurisdiction does not suffice to avoid preemption. Similarly, while finding that measures requiring or authorizing immigration status checks by state and local officers are not facially preempted, the Court suggested that the application of such measures could lead to new constitutional challenges.