WASHINGTON — The Supreme Court on Monday seemed sharply divided during an extended argument over a challenge to President Obama’s plan that would shield millions of undocumented immigrants from deportation and allow them to work in the country legally.
Much of the argument was technical, but the justices occasionally paused to acknowledge realities outside the courtroom. Justice Stephen G. Breyer said the case had enormous political implications. Justice Sonia Sotomayor said that about 11 million immigrants live “in the shadows.”
“They’re here whether we want them or not,” Justice Sotomayor said.
The case, brought by 26 states, may produce a significant ruling on presidential power and immigration policy in the midst of a presidential campaign in which both issues have been prominent.
Solicitor General Donald B. Verrilli Jr., the government’s top appellate lawyer, opened the arguments with a vigorous defense of Mr. Obama’s authority to set priorities for immigration enforcement, but within minutes he was challenged by Chief Justice John G. Roberts Jr. and several of the court’s other members.
Justice Anthony M. Kennedy questioned whether the president can defer deportations for millions of people without specific congressional authorization, saying “that is a legislative task, not an executive task.”
“It’s as if the president is defining the policy and the Congress is executing it,” Justice Kennedy said. “That’s just upside down.”
In making his case, Mr. Verrilli asserted that the state of Texas should not be allowed to challenge the president’s actions by claiming that it would cost the state money to give driver’s licenses to the millions of immigrants affected by the federal policy. Mr. Verrilli argued that Texas could simply change its law to deny driver’s licenses to the immigrants.
“You would sue them instantly,” Chief Justice Roberts said as he repeatedly questioned the government’s arguments.
He also pressed Mr. Verrilli on whether the president could simply deem all illegal immigrants to be legally present under the new policy. Mr. Verrilli said there were statutory constraints that would prevent the president from doing so.
Scott A. Keller, Texas’s solicitor general, said Mr. Obama’s plan was unprecedented and unlawful. He faced skeptical questions from the court’s more liberal members about whether his state had suffered the sort of direct and concrete injury that gave it standing to sue.
The case, United States v. Texas, No. 15-674, was heard by an eight-member court, and the absence of Justice Antonin Scalia, who died in February, has altered the judicial dynamic. A 4-4 deadlock is now a live possibility, one that would leave in place an appeals court ruling that blocks the plan without setting a Supreme Court precedent.
When the court agreed in January to hear the case, it raised the possibility of a broad decision by taking the unusual step of asking the parties to address whether Mr. Obama had violated his constitutional obligations to enforce the nation’s laws. This month, the court granted a lawyer for the House of Representatives, which supports the challengers, 15 minutes to present arguments on that issue.
But a broad ruling on the scope of presidential power seems unlikely to emerge from a short-handed court.
The states challenging Mr. Obama’s immigration plan say he has repeatedly taken unilateral and unlawful action to sidestep Congress on gun control, gay rights, the minimum wage, contraception and climate change. White House and Justice Department officials have defended Mr. Obama’s approach as legal and valuable.
Monday’s case concerns a program intended to allow as many as five million unauthorized immigrants who are the parents of citizens or of lawful permanent residents to apply for a program sparing them from deportation and providing them work permits. The program, announced in November 2014, was called Deferred Action for Parents of Americans and Lawful Permanent Residents, or DAPA.
The line for one of the coveted red tickets that allow members of the public into the Supreme Court for the oral arguments stretched around the block on Monday. Some groups had been camping in front of the court since Friday night, eager for a chance to witness history.
Some members of Susana Sandoval’s group, Dreamer’s Mothers in Action, had come from as far as Michigan — and some of them had fasted all weekend in a show of support of the president’s executive actions.
“This is just a little bit of sacrifice for the four to five million people that will benefit from this,” Ms. Sandoval said.
Groups of young people walked up and down the sidewalk holding banners and chanting mantras like “Sí se puede,” the Spanish version of one of Mr. Obama’s 2008 campaign slogans — “Yes we can.”
Thomas Pittman, a retired firefighter and a deacon at Shiloh Baptist Church in Trenton, said he was looking for the effect the case might have on the presidential race. “I think it’s going to have a major impact on the election, due to the fact that Trump wants to deport people and close our borders down,” he said, referring to the Republican front-runner, Donald J. Trump.
Mr. Obama has said he took action after years of frustration with Republicans in Congress who had repeatedly refused to support bipartisan Senate legislation to update immigration laws. A coalition of 26 states, led by Texas, promptly challenged the plan, accusing the president of ignoring administrative procedures for changing rules and of abusing the power of his office by sidestepping Congress.
In February 2015, Judge Andrew S. Hanen of Federal District Court in Brownsville, Tex., entered a preliminary injunction shutting down the program while the legal case proceeded. The government appealed, and a divided three-judge panel of the United States Court of Appeals for the Fifth Circuit, in New Orleans, affirmed the injunction.
If the Supreme Court upholds Mr. Obama’s actions, the White House has vowed to move quickly to set up the program and begin enrolling immigrants before his successor takes over early next year. Democratic presidential candidates have said they would continue the program, but most of the Republicans in the race have vowed to dismantle it and redouble immigration enforcement.
In their Supreme Court briefs, the states acknowledged that the president has wide authority over immigration matters, telling the justices that “the executive does have enforcement discretion to forbear from removing aliens on an individual basis.” Their quarrel, they said, was with what they called a blanket grant of “lawful presence” to millions of immigrants, entitling them to various benefits.
In response, Mr. Verrilli told the justices that “lawful presence” is merely what has always followed from the executive branch’s decision not to deport someone for a given period of time.
“Deferred action does not provide these individuals with any lawful status under the immigration laws,” he said. “But it provides some measure of dignity and decent treatment.”
“It recognizes,” Mr. Verrilli added, “the damage that would be wreaked by tearing apart families, and it allows individuals to leave the shadow economy and work on the books to provide for their families, thereby reducing exploitation and distortion in our labor markets.”
If the states are to prevail, they must show that they have suffered the sort of direct and concrete injury that gives them standing to sue.
Judge Jerry E. Smith, writing for the majority in the appeals court, focused on one injury said to have been suffered by one state, Texas, which he said would have to spend millions of dollars to provide driver’s licenses to immigrants as a consequence of the federal program.
self-inflicted, a product of its own decision to offer driver’s licenses below cost and to tie eligibility for them to federal standards.
Texas responded that being required to change its laws was itself the sort of harm that confers standing. “Such a forced change in Texas law would impair Texas’s sovereign interest in the power to create and enforce a legal code,” the state said in a brief.