A federal appeals court is hearing arguments Wednesday over whether to allow Texas to temporarily enforce its controversial law that allows state officials to arrest and detain people they suspect of entering the country illegally.

The hearing comes one day after the Supreme Court cleared the way for the measure to take effect, only for it then to be blocked by the 5th US Circuit Court of Appeals late Tuesday night.

The law, SB 4, is part of the ongoing battle between Texas and the Biden administration over border policy and the flow of migrants into the United States. Immigration enforcement, generally, is a responsibility of the federal government, but the law signed by Republican Gov. Greg Abbott in December makes entering Texas illegally a state crime and allows state judges to order immigrants to be deported.

The law was initially challenged by the Biden administration, a pair of immigration advocacy groups and El Paso County, all of which have stressed throughout the litigation that the entry and removal of migrants has long been within the federal government’s bailiwick.

For its part, Texas has argued that SB 4 “comports with federal law” and claims that “states generally enjoy wide latitude to regulate alien misconduct and prosecute crimes involving illegal entry.”

Appeals court judge: ‘I’m not sure I understand the law totally’

In the first part of the hearing Wednesday, 5th Circuit Chief Judge Priscilla Richman pressed an attorney for Texas on how the state’s controversial immigration law would work, and the attorney has struggled with his answers.

Texas Solicitor General Aaron Nielson admitted to the judge he is not entirely sure how Texas state courts would interpret the law, as he noted that a trial judge blocked it before it could be put into effect.

“I was just trying to envision how this would all play out. I’m not sure I understand the law totally,” the judge said.

Neilson repeatedly was unable to address scenarios she laid out as the judge tried to understand how the law would work. He repeatedly pointed to comments from federal officials, including from President Joe Biden, that there’s a “crisis” at the border.

Richman, a George W. Bush nominee, will be the key vote for Texas on the three-judge panel in its efforts to revive its law while the legal challenges to it play out. So far she has shown skepticism towards the state law.

“This is the first time, it seems to me, that a state has claimed that they have the right to remove illegal aliens. I mean, this is not a power that historically has been exercised by states, has it?” Richman said.

DOJ says immigration policy is an ‘international exercise’

A Justice Department lawyer said that immigration policy is “fundamentally an international exercise” as he pressed to keep the law frozen.

DOJ attorney Daniel Tenny said implementing immigration policy involves collaboration with other countries. He was responding to a question from Richman, who asked him to address Texas’ assertions that the state law should be allowed to go into effect because the federal government is not doing a sufficient job carrying out US immigration laws.

Tenny said those claims were flawed both legally and factually.

Trump nominee presses Justice Department

Tenny has faced persistent questioning from Circuit Judge Andrew Oldham, an extremely conservative judge appointed by former President Donald Trump. Oldham has asked questions suggesting skepticism of a lower court’s decision to block the entire state law, rather than the specific parts of it that have been singled out by DOJ as conflicting with federal law.

Much of the questioning towards the Justice Department has focused on a Supreme Court case that blocked an Arizona immigration law that was nicknamed the “show me your papers” law.

The Justice Department argues that the precedent the Supreme Court set in that case requires the Texas immigration law to be blocked. But Oldham has expressed doubt. He suggested the entirety of the Arizona law was in conflict with federal immigration prerogatives, but that there are parts of the Texas immigration law that do not overlap with federal authority on immigration.

Oldhman, who already said in an order Tuesday night that he would have let the Texas law go into effect for the time bring, appears to be trying to draw distinctions between the Texas case and the Arizona case.

Supreme Court let law take effect for several hours Tuesday

The Supreme Court did not explain its reasoning Tuesday when it voted to let the law take effect pending further action from the 5th Circuit.

However, a concurring opinion written by Justice Amy Coney Barrett, joined by Justice Brett Kavanaugh, explained that the appeals court had handed down only a temporary “administrative” order. Barrett appeared eager to keep the Supreme Court out of reviewing such orders.

Barrett and Kavanaugh, two critical votes on the high court, wrote that the justices should stay out of second-guessing appeals courts when it comes to very short-term “administrative” pauses that are generally used to give courts a few additional days to review the briefs.

“The time may come, in this case or another, when this court is forced to conclude that an administrative stay has effectively become a stay pending appeal and review it ac­cordingly,” she wrote. “But at this juncture in this case, that conclusion would be premature.”

Barrett wrote that if the 5th Circuit doesn’t issue a decision soon, the Biden administration and the other parties in the case could return to the Supreme Court.

The 5th Circuit scheduled Wednesday’s arguments shortly thereafter.

The three liberal justices dissented, saying the law should remain blocked.

Justice Sonia Sotomayor, whose dissent was joined by Justice Ketanji Brown Jackson, said the order “invites further chaos and crisis in immigration enforcement.”

The law, Sotomayor wrote in her dissent, “upends the federal-state balance of power that has existed for over a century, in which the National Government has had exclusive authority over entry and removal of noncitizens.”