WASHINGTON, D.C. — The Supreme Court’s conservative justices sounded skeptical Tuesday about the legality of an Obama-era policy that has allowed 700,000 young immigrants to live and work in the United States, suggesting they may clear the way for President Donald Trump to terminate the program.

Chief Justice John G. Roberts Jr., whose vote is likely to be the deciding one, asked questions of both sides and did not tip his hand, but he appeared to agree with the Trump administration’s position that the program was legally questionable.

U.S. Solicitor General Noel Francisco urged the justices to toss out rulings from three federal judges and to allow the president to “wind down” the program known as Deferred Action for Childhood Arrivals, or DACA.

Francisco called DACA “a temporary stopgap measure” that could be repealed at any time. The administration has also argued that the original program was illegal because it exceeded the powers of the president.

At several points, Roberts suggested that the Trump administration may be on firm ground in thinking DACA was illegal. He noted that a similar, more far-reaching immigration order by President Barack Obama —protecting immigrants who are parents of some U.S. citizens or lawful residents —had been blocked by the 5th Circuit and the Supreme Court in a tie vote. “Isn’t that enough?” Roberts asked.

Arguing in defense of the so-called Dreamers and their right to work legally was Ted Olson, who served as U.S. solicitor general under President George W. Bush. Olson argued that rescinding DACA would “trigger disruption” to the lives of hundreds of thousands of people, their families, businesses and the armed forces.

Both Olson and California Solicitor General Michael Mongan argued that DACA was legal, and the Trump administration could not shut it down solely on the basis that it was illegal.

The court’s four liberal justices asked skeptical questions of Trump’s lawyers, suggesting they would vote to affirm rulings by three judges who had blocked the repeal. But it was unclear they would have a fifth vote from one of the conservatives.

Though some justices questioned whether Trump’s termination of the DACA program was even something that the courts could or should review, Roberts appeared to disagree with Francisco’s claim that the Trump’s repeal was off limits to judicial review.

More than a quarter of those protected under the DACA program live in California, and many of them are raising families. But they could be left without a work permit next year if the high court rules for Trump.

The case poses an unusual test of presidential power. Trump’s lawyers argued he should prevail because Obama abused his executive authority by granting a temporary exemption from deportation for immigrants who were brought to this country as children.

For more than two years, Trump has been seeking to end the special protections for the Dreamers put in place by Obama, but he has been blocked by federal judges in San Francisco, New York and Washington, D.C. All three said the proposed repeal was flawed because it relied on the false claim that Obama’s policy was illegal from the start.

Obama announced the special protection for the Dreamers in 2012, and the policy has gained steadily in popularity. Opinion polls in the past year have found that more than three-fourths of those surveyed —both Republicans and Democrats —support granting legal status to the Dreamers.