The last oral argument of the U.S. Supreme Court’s term was an explosive one, as the justices considered whether SB 1070, the controversial Arizona immigration statute, is preempted by federal law.

But with four of the eight justices who heard the case indicating that they favor upholding at least part of the law (Justice Elena Kagan recused herself, presumably due to her work on the case as solicitor general), the Obama administration may have to hope for a tie. That result would in effect be a win, because it would allow a lower court ruling blocking the law’s implementation to stand.

SB 1070 requires local law enforcement officers to check the immigration status of detained individuals if there is reasonable suspicion they are in the country illegally, criminalizes the violation of federal registration laws by undocumented immigrants, makes it a crime for undocumented workers to seek or hold employment and authorizes the warrantless arrest of persons suspected of committing removable offenses if there is probable cause.

The measure has drawn nationwide attention, with opponents arguing the law tramples on federal authority and even encourages racial profiling by police.

But some Arizona state officials and their supporters say the measure is a necessary enforcement tool that can coexist with federal law, and is necessary to stem the tide of illegal immigration at a time where federal enforcement has been lacking.

The Obama administration launched a federal court challenge to block the law from being implemented, arguing that the field of immigration law and enforcement was occupied by the federal regulatory scheme, and that the law conflicted with federal objectives.

The 9th Circuit upheld a lower court ruling blocking the law’s implementation.

At oral argument in April, Paul D. Clement, a partner in the Washington office of Bancroft representing Arizona, called the administration’s challenge to the law an “extraordinary step.”

“A state does not need to point to federal authorization for its enforcement efforts,” Clement told the justices.

But Solicitor General Donald B. Verrilli Jr. argued that allowing states to implement their own immigration laws would frustrate the federal scheme. Measures similar to SB 1070 have been introduced in 36 states, and signed into law in five.

“The entire country feels the effects of [this] conduct by an individual state,” Verrilli told the court. “And that’s why the power needs to be exercised at the national level and not the state level.”

Fourth Amendment issues

As protesters on both sides of the issue held signs and chanted in English and Spanish on the sidewalk at the foot of the court’s grand marble staircase, inside the courtroom the justices parsed each provision of the law separately – an indication that they could strike some components of the statute while leaving others in place.

Clement argued that the federal Immigration and Nationality Act “goes out of [its] way to try to facilitate state and local efforts to communicate with federal immigration officials in order to ascertain the immigration status if individuals.”

Therefore, he argued, the government’s claim that the state law conflicts with the federal scheme fails.

But Justice Anthony M. Kennedy – who could potentially cast the deciding vote in the case – asked if the state statute gives law enforcement officials the ability to hold individuals for long periods of time while ascertaining their immigration status.

“If it takes two weeks to make that determination, can an alien be held by the state for that whole period of time?” Kennedy asked.

“I don’t think so,” Clement said. “You have the Fourth Amendment backing up those limits.”

When Justice Stephen G. Breyer inquired more into Fourth Amendment limits, Justice Antonin G. Scalia asked: “Is this an immigration problem or is this a Fourth Amendment problem?”

“The federal government [is] not making a Fourth Amendment claim here,” Clement said. “And it’s neither an immigration law concern nor something that should be the basis for striking down a statute on its face.”

‘Not about racial profiling’

Before Verrilli could utter a word of argument, Chief Justice John G. Roberts Jr. made a rather dramatic clarification.

“Before you get into what the case is about, I’d like to clear up at the outset what it’s not about. No part of your argument has to do with racial or ethnic profiling, does it?” Roberts asked. “I saw none of that in your brief.”

“That’s correct,” Verrilli said, arguing instead that the case was about “the Constitution vest[ing] exclusive authority over immigration matters with the national government.”

When asked about the power of states to exclude illegal aliens, Verrilli said that power rests with federal, not state, authorities.

“The Constitution vests exclusive authority over immigration matters with the national government,” Verrilli asserted.

“All that means is that the government can set forth the rules concerning who belongs in this country,” Scalia retorted. “But if, in fact, somebody who does not belong in this country is in Arizona, Arizona has no power? What does sovereignty mean if it does not include the ability to defend your borders?”

But it was Roberts, not Scalia, who posed the toughest line of questions to Verrilli, indicating he was leaning strongly in favor of Arizona’s position.

“You say that the federal government has to have control over who to prosecute, but I don’t see how [the status check provision] says anything about that at all,” Roberts said to Verrilli. “[The] discretion to prosecute for federal immigration offenses rests entirely with the attorney general.”

“That is true, but I think it doesn’t get at the heart of the problem here,” Verrilli replied, arguing that the state provision usurps federal authorities’ ability to prioritize immigration enforcement actions.

He also said the law leads to “harassment.”

“We are not making an allegation of racial profiling,” Verrilli said. “Nevertheless … given that you have a population in Arizona of 2 million Latinos, of whom only 400,000 at most are there unlawfully … ”

“Sounds like racial profiling to me,” Scalia interjected.

When Verrilli ran into trouble making the argument that state officials have the ability to cooperate with federal immigration enforcement, but not to pass immigration enforcement laws, Sotomayor – who appeared to support the federal government’s position – tried to help him out.

“You can see it’s not selling well,” she said. “Why don’t you try to come up with something else?”

Brewer asserts ‘right to protect’

After oral arguments, Gov. Jan Brewer told reporters that she signed SB 1070 into law “to address the terrible situation Arizona was facing” with respect to illegal immigration, and said she knew then it would be subject to a challenge that could go all the way to the Supreme Court.

But she said she was confident that the justices would uphold the measure.

“As governor, I had a right to protect the citizens of Arizona,” Brewer said, adding that SB 1070 “basically mirrors federal law.”

A decision is expected before the end of the court’s term.