The Supreme Court is poised to weigh in on the future of some 660,000 immigrants brought to the U.S. illegally as children in yet another politically fraught debate on the limits of President Donald Trump's authority.

The justices on Tuesday will hear oral arguments from three consolidated cases challenging the Trump administration's efforts to shut down the Deferred Action for Childhood Arrivals program, known as DACA. The arguments mark the culmination of a yearslong fight over the Obama-era program which has extended protections against deportation to young immigrants brought to the country illegally as children.

The court's opinion is expected next year just months before the 2020 election in which immigration and, specifically, DACA will likely feature as touchstone issues. Should the high court side with the Trump administration, allowing it to dismantle the program, recipients could be at risk of deportation.

Ending the program is a priority for the Trump administration as it pursues a policy agenda that includes restricting legal and immigration. Critics of the program say it rewards and encourages illegal immigration and hurts American workers. It has been frequently held up by Trump and other officials as an example of what they see as President Barack Obama's executive overreach.

Under the program, which was created in 2012, young immigrants who meet a number of qualifications are protected from deportation for two years and are granted work authorization. They must renew their status when it expires. Janet Napolitano, the secretary of homeland security at the time, described the program as an exercise of "prosecutorial discretion."

Hundreds of thousands of immigrants have enrolled in the program since it was created. Of the nearly 700,000 current recipients, many work or are in school, and their median age is 25, according to government data.

But status recipients have been living in limbo since September 2017 when the Trump administration ended the program. A number of federal courts, however, blocked the Trump administration from doing so, ruling that the White House provided inadequate reasons for terminating the program. Recipients can currently renew their status, but the federal government is not accepting new applications.

Now the high court will have the final say. The justices will not necessarily rule on the legality of the program but rather the legality of the Trump administration's efforts to end it. At issue are two central questions: if the Trump administration's effort to unravel the protections is reviewable by the court and if the move to terminate the program is "arbitrary and capricious," or unreasonable, in violation of a federal law that sets standards for agency actions.

The Trump administration argues that the decision is not reviewable by the courts because of agency discretion. And, even if the decision is reviewable, the administration argues that its reasoning for ending DACA was legitimate. The administration says it ended the program over concerns that it was unconstitutional and an overreach of executive authority. The government maintains it is illegal.

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The plaintiffs, on the other hand, say the decision to stop the program is reviewable by the courts, and they argue that the reasoning behind the decision was invalid. To rebut the government's claim that it was concerned the program is unconstitutional, the plaintiffs point out that the federal government exercises broad discretion in immigration policy enforcement all the time, deciding who to deport or granting relief to certain immigrants or groups of immigrants. The program, the plaintiffs say, fits well within the limits of that discretion.

Napolitano, who, as homeland security secretary, signed the memorandum establishing the program, is now one of the plaintiffs suing to protect it. Napolitano is the president of the University of California system, which challenged the Trump administration in court over the program's termination in part because its termination would affect a large number of University of California students. That case is one of the three before the high court.

Napolitano says the program was crafted "from the get-go within the authority of the executive branch." The Justice Department at the time opined that the program was legal as long as immigration officials had discretion over individual applicants.

"There is a long line of precedent saying that the executive branch has what's called prosecutorial discretion under the reality that the executive does not have the resources to enforce all laws against everybody who's a possible violator," Napolitano says.

"And using that theory and thinking about these young people who have grown up in the United States – who really only know the U.S. as home and may not even speak the language of their country of origin – it seemed to me that this was the last group that we would want to enforce the immigration laws against," she says.

Avidan Cover, a law professor and the director of the Institute for Global Security Law and Policy at Case Western Reserve University Law School, says the plaintiffs are correct that the Trump administration regularly exercises discretion in immigration enforcement but predicts that it will be difficult to convince a majority of the justices that the Trump administration's reasons for ending DACA – including the rationale that the government believes the program to be illegal – were arbitrary and capricious. The plaintiffs' argument also leaves open the possibility that the government could come back with other reasons for ending the program that would be acceptable to the courts, Cover says.

But the government's argument contains an interesting paradox, Cover says. Underlying the administration's argument that it has the power to rescind the program is an argument that it is an overreach of executive authority.

"By saying DACA is illegal, you're limiting the president's power and discretion over immigration matters," Cover says, noting that it is an especially noteworthy argument given that the Trump Justice Department has gone to bat in the past for an expansive view of executive authority, including in the case of the so-called travel ban.

"This wouldn't be the first president or the first Justice Department to try to have it both ways. But it is interesting to see arguments for great levels of discretion in one context – or very much, you could argue, the same context – and then here it's a very limited one."

The court split 4-4 in 2018 in a similar case concerning a program shielding the immigrant parents of citizens and legal residents. That ruling, which occurred while only eight justices sat on the court due to the death of Justice Antonin Scalia, affirmed a lower court's decision to block the program and could foreshadow how the court will decide on DACA. With the addition of Justice Brett Kavanaugh, the court is composed of five justices who are considered to be more conservative and four justices who are regarded as more liberal.

While the court battle has dragged on, Congress has been at a standoff over the future of young immigrants despite polls showing overwhelming public support for the program and for extending permanent protections to recipients.

The program has instead been used as a bargaining chip in congressional negotiations over funding and immigration policy. Democrats staunchly support it and back plans to extend protections and provide a path to citizenship for recipients – a position Republicans and the White House have tried to leverage in order to secure funding for Trump's southern border wall and other immigration initiatives.

Trump rejected a deal from Democrats in January 2018 that would have given the president $25 billion in border wall funding in exchange for a path to citizenship for young immigrants. And during a government shutdown a year later, Trump said he would give youths three more years of protection if Democrats allocated $5.7 billion in funding for a wall, but Democrats refused the offer.

The House earlier this year passed legislation to protect young immigrants and offer them a path to citizenship, but the Republican-held Senate has not taken up the bill.

Absent any congressional action, the fate of the young immigrants is left up to the Supreme Court. The case is one of the most anticipated and high-profile of the current term, and large crowds of activists, program recipients and other members of the public are expected to congregate in front of the court Tuesday. Among those expected to attend will be a group of recipients and activists who completed a 230-mile march from New York City to Washington, D.C., to raise awareness and advocate for immigrants.