The administration is seeking to overturn a Texas-based federal judge's ruling in June that blocked the policy nationwide. It had been in effect for less than a year.
Over more than two hours of oral argument, however, there was little sign that the nine justices were close to an outcome that would garner a majority vote as they grappled with a series of complex and interlinked legal questions.
Announced in September 2021, President Joe Biden's plan marked a shift away from the hard-line enforcement approach taken by former President Donald Trump. The administration argued that with an estimated 11 million immigrants in the U.S. illegally, the government has to prioritize certain cases because it does not have the resources to detain and deport all of them.
Texas and Louisiana immediately challenged the plan in court, arguing that federal immigration law requires that certain illegal immigrants — including those convicted of aggravated felonies, human trafficking and some gun crimes — must be detained after they are released from criminal custody. Biden's policy, which required an individual assessment of whether an immigrant is a threat to public safety or national security while the government initiates the deportation process, would defy that requirement, the states say.
Biden administration lawyers argue that the president has broad discretion to set enforcement priorities.
Among the legal questions is whether the states had legal standing to bring the challenge and, if they did, whether the guidelines are unlawful. A third question concerns whether the judge had the authority to block the policy even if it is unlawful.
Based on questions asked by the justices, it appeared the court would most likely find that states had standing, but they seemed more tentative about the extent to which the government's hands are tied on immigration policy by either Congress or courts.
On one hand, several justices pointed out that the federal government lacks the resources to detain every illegal immigrant agents encounter, regardless of what Congress says.
"It's impossible for the executive [branch] to do what you want it to, right?" Chief Justice John Roberts asked Texas Solicitor General Judd Stone.
Justice Elena Kagan said it would be "extraordinarily onerous" to impose a requirement that the government must apprehend all immigrants in the country illegally. She noted that immigration is an area courts have traditionally viewed as being at "the zenith of executive power."
On the other hand, Roberts said, if Congress requires the executive branch to do something even if it cannot be done, "should we still fulfill our responsibility to say what the law is?"
The court did not seem divided along ideological lines, with some conservative justices indicating support for the Biden administration's argument that the judge lacked authority to block the policy nationwide in June.
Conservatives were less sympathetic toward the government's argument that the states lacked legal standing to challenge the policy, with Justice Brett Kavanaugh saying it could open the door to future administrations’ refusing to enforce environmental and labor laws, among other things.
If states cannot sue, it would be left to Congress to take action, such as by refusing to fund the government or impeaching the president, he added.
“It’s forcing Congress to take dramatic steps,” Kavanaugh said.
One possible outcome is that the court could say the government policy was unlawful but find that the judge did not have authority to throw out the policy nationwide.
In the ruling blocking the policy, U.S. District Judge Drew Tipton — a Trump appointee — said Texas had standing because it could show that immigrants who should have been detained were in Texas and in some cases had committed crimes.
Tipton found both that the policy was unlawful and that the government failed to follow the correct procedure in implementing it.
Republicans have frequently accused Biden of a lax approach to enforcement and border security, which they argue have led to a rise in crime and an increase in the number of people entering the U.S. illegally.
The Supreme Court voted 5-4 in July to reject the Biden administration’s request to immediately restore the policy but agreed to hear oral arguments. A ruling is due by the end of June.
This article was originally published on NBCNews.com