The U.S. Supreme Court Monday upheld the "stop and check" provision of Arizona's law aimed at curbing illegal immigration.

By a 5-3 vote, with Justice Elena Kagan not participating, the court struck down three other key provisions.

That led a court watcher on "SCOTUSblog" to call it "a significant win for the Obama Administration. It got almost everything it wanted."

Struck down were provisions that would have made it a crime for immigrants without work permits to seek employment, would have made it a crime for immigrants to fail to carry registration documents and would have allowed police to arrest immigrants they believe have committed deportable offenses.

"The national government has significant power to regulate immigration," Justice Anthony Kennedy wrote in the court's majority opinion. "With power comes responsibility, and the sound exercise of national power over immigration depends on the nation's meeting its responsibility to base its laws on a political will informed by searching, thought­ful, rational civic discourse.

"Arizona may have understandable frustrations with the problems caused by illegal immigration while that process continues, but the state may not pursue policies that undermine federal law."

Justice Antonin Scalia wrote in a dissenting opinion: "As a sovereign, Arizona has the inherent power to ex­clude persons from its territory, subject only to those limitations expressed in the Constitution or constitution­ ally imposed by Congress."

Justice Samuel Alito said he favored upholding the full Arizona law as passed.

Read the full opinion here

-- The reactions --

Arizona Gov. Jan Brewer, who signed the law and sat in on the oral arguments before the court in April, declared victory in a prepared statement.

"Today's decision by the U.S. Supreme Court is a victory for the rule of law," Brewer's statement said in part. "It is also a victory for the 10th Amendment and all Americans who believe in the inherent right and responsibility of states to defend their citizens. After more than two years of legal challenges, the heart of SB 1070 can now be implemented in accordance with the U.S. Constitution."

In an 11 a.m. news conference Monday, Brewer commented further. She claimed the court upheld the "heart of the law," and that the ruling represented "a day we've been waiting for."

President Obama said in a statement that he was worried that the "stop and check" provision remained intact, but said he was pleased about the rest of the decision.

"I am pleased that the Supreme Court has struck down key provisions of Arizona's immigration law," Obama's statement said. "What this decision makes unmistakably clear is that Congress must act on comprehensive immigration reform. A patchwork of state laws is not a solution to our broken immigration system – it’s part of the problem."

Republican presidential candidate Mitt Romney, in a statement, used the ruling to criticize Obama.

"Today's decision underscores the need for a president who will lead on this critical issue and work in a bipartisan fashion to pursue a national immigration strategy," Romney said in the statement. "President Obama has failed to provide any leadership on immigration. This represents yet another broken promise by this president."

U.S. Rep. Raúl Grijalva, D-Ariz., an outspoken critic of SB 1070, characterized his feelings as "mixed."

"I thought that the parts the Supreme Court struck down as unconstitutional and preempted by the Constitution were important," Grijalva said in an interview, "for no other reason than to say that this immigration reform is a national, federal responsibility and that Congress was admonished by the court to do its job."

-- The decision --

The court upheld Arizona's case that state and local police can ask someone's immigration status when the person is stopped for "reasonable cause." But it left open the possibility of further challenge once that aspect of the law is implemented.

The provision is one that civil rights organizations have complained will lead to racial profiling of Latinos, including the 1.5 million Latinos who are Arizona and U.S. citizens or who otherwise are here legally.

Under the provision, state and local law-enforcement officers are obliged to ask anyone they suspect of being in the country illegally for documentation to prove their legal status.

Such a request can come only after a person has been stopped for reasonable cause in connection with another action and not because of their racial or ethnic appearance "except to the extent permitted" by the U.S. and state constitutions.

The law was passed two years ago by the Legislature and signed by Gov. Jan Brewer. Almost immediately, several individuals and entities challenged it, including the U.S. Justice Department.

The federal case was predicated on preemption, the legal argument that control of immigration and laws surrounding it are an exclusive purview of the federal government.

State officials argued that SB 1070 did not usurp federal authority but only enhanced it by specifically directing state and local law-enforcement agencies and officers to enforce federal immigration laws.

Civil rights organizations, including many Latino groups, argued that the law would open the way to discrimination based on people's appearance, something they said already was occurring in Maricopa County in immigration sweeps by the Sheriff's Department.

State officials said the law banned such racial profiling, and that issue did not become a part of the federal case.

With the "stop and check" aspect of the law now in place, the American Civil Liberties Union of Arizona is expected to reactivate its challenge of the law, arguing that it violates individuals' First, Fourth and 14th Amendment rights.

ACLU of Arizona Legal Director Dan Pochoda, who is handling the civil rights case, said in an interview with Arizona Public Media last week that if "stop and check" goes into effect, "it will violate the Fourth Amendment or other rights." See his full interview here.

Political, immigration and civil rights groups across the country reacted to the ruling, including the National Association of Latino Elected and Appointed Officials, which just last week heard from Obama and Romney, both speaking on immigration, at the NALEO annual convention in Florida.

“NALEO applauds the court’s action to prevent the state from unconstitutionally criminalizing being undocumented, seeking or engaging in work, or being deportable," the organization said in a statement. "NALEO is extremely concerned, however, that Arizona’s “show-me-your-papers” policy was not yet determined to be unconstitutional because it is unclear how it will be implemented."

Justice Kagan did not participate in the case because of a potential conflict based on her service in the U.S. Solicitor General's Office when the federal case was filed two years ago. The Solicitor General is the legal representative of the federal government.