WASHINGTON — One of President Biden’s most ambitious proposals — a $400 billion program to forgive student loan debt for 40 million Americans — could become the latest victim of a legal tug of war with the Supreme Court over the powers of the presidency.
Conservative justices on the court signaled Tuesday that they are deeply skeptical that Mr. Biden has the power to wipe out such a vast amount of student debt. In oral arguments, several justices said they believed a program that costs so much and affects so many people should have been more explicitly approved by Congress.
It was not the first time the court has suggested that Mr. Biden overstepped his authority, but the case has the potential to curtail Mr. Biden’s ambitions just as newly empowered Republicans in the House have vowed to block his every move in Congress.
During Mr. Biden’s first two years in office, the court has blocked him from enacting key parts of his agenda, including sweeping measures to address climate change, vaccine requirements at large companies and a ban on evictions during the pandemic.
In each case, the court’s conservative majority said the president needed clear congressional approval to pursue such major policies.
The court’s decision on whether to block the student loan program as well, which is likely to come by summer, will have a vast impact on millions of borrowers who have struggled to pay back their loans.
And it will set additional legal precedents, potentially defining new limits for presidential power.
The ruling could have other broad political implications, forcing Mr. Biden and his allies to reshape their efforts to court one of the Democratic Party’s most important constituencies ahead of the 2024 campaign: young people.
Instead, the president may have to face the voters with a very different message: that despite his best efforts, student debt relief was thwarted by Republicans who blocked his policy at the Supreme Court.
Asked on Wednesday whether he was confident that the court would rule in the administration’s favor, Mr. Biden said: “I’m confident we’re on the right side of the law. I’m not confident about the outcome of the decision yet.”
The White House is not conceding defeat. In court on Tuesday, lawyers for Mr. Biden’s administration argued that Congress had already given the secretary of education the authority to forgive student debt.
But Mr. Biden’s team has already shown its willingness to use the issue for its own political advantage, even if the best it can do is blame Republicans for stopping the plan.
Miguel A. Cardona, the secretary of education, on Tuesday sent an email to tens of millions of Americans who had signed up for relief.
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“While opponents of this program would deny relief to tens of millions of working- and middle-class Americans,” Mr. Cardona wrote in the email, “we are fighting to deliver relief to borrowers who need support as they get back on their feet after the economic crisis caused by the pandemic.”
If the court blocks the program, the administration can continue to use the email list to communicate with millions of potential voters about why they are not getting the relief that Mr. Biden and his team had promised.
Max Lubin, the chief executive of Rise, a group that has advocated for student debt relief, said the president has a good argument to make if Republicans succeed in blocking his debt relief program.
He said the White House could send a message that “you have an alternative in us and we have your back.”
Mr. Lubin added: “I think that’s a really powerful message to send to 25-year-olds.”
Last summer, when he announced his plan, Mr. Biden said student loan forgiveness was critical because “an entire generation is now saddled with unsustainable debt in exchange for an attempt, at least, at a college degree.”
But without a large congressional majority to pass such Democratic priorities, the president has repeatedly turned to executive action, prompting legal objections from his Republican opponents.
Those objections have made their way to a Supreme Court, whose membership now includes six conservative justices and three liberal ones. That has left the president on the losing side of several significant cases.
The Biden administration’s fraught relationship with the Supreme Court has its roots in a case in which the justices ruled against President Donald J. Trump, as Chief Justice John G. Roberts Jr. said during Tuesday’s arguments.
In that 2020 case, it was liberals who urged the Supreme Court to prevent Mr. Trump from abruptly ending an Obama-era program from 2012 that protected about 700,000 young immigrants from immediate deportation.
“The case reminds me of the one we had a few years ago under a different administration where the administration tried acting on its own to cancel the Dreamers program, and we blocked that effort,” he said. “And I just wonder, given the posture of the case and given our historic concern about the separation of powers, you would recognize at least that this is a case that presents extraordinarily serious, important issues about the role of Congress?”
That case was decided by a 5-to-4 vote, with the chief justice joining what was then a four-member liberal wing to form a majority. In dissent, Justice Clarence Thomas predicted that subsequent administrations would face similar legal hurdles.
“It has given the green light,” he wrote of the court, “for future political battles to be fought in this court rather than where they rightfully belong — the political branches.”
Mr. Biden’s struggles over the past two years — including in this week’s student loan case — suggest that Justice Thomas was right in his prediction. After rejecting Mr. Trump’s executive authority in 2020, the court is now doing the same for Mr. Biden.
The administration’s track record has been mixed.
In December, the justices said that Title 42, a pandemic-era health measure that restricted entry at the southern border, must temporarily remain in place. In June, though, the court ruled that the administration could rescind a Trump-era immigration program that forced certain asylum seekers arriving at the southwestern border to await approval in Mexico.
And, in a modest victory for Mr. Biden, the court did allow a more limited mandate requiring health care workers at facilities receiving federal money to be vaccinated.
In the student loan case on Tuesday, a majority of the justices appeared ready to place another limitation on how far Mr. Biden can go in responding to the ripples of the pandemic. At issue is Mr. Biden’s use of a law designed to allow student loan waivers during national emergencies.
But court observers said the president could still win the case on technical grounds if the justices decide that the plaintiffs in the case — Republican state attorneys general and two student loan borrowers — do not have the proper standing to sue.
On Wednesday, Karine Jean-Pierre, the White House press secretary, refused to offer a backup plan if the administration loses.
“We do not have another plan,” she told reporters. “This is our plan. This is it. We believe that we have the legal authority. That’s why we took it to the highest court in the land, the Supreme Court. And we’re going to continue to fight.”