A court rules that the Trump administration illegally used military funds for the border wall.

SAN FRANCISCO — A federal appeals court decided 2-1 Friday that the Trump administration violated the law by using military money to build a wall at the southern border of Arizona, New Mexico and California.

A panel of the 9th U.S. Circuit Court of Appeals said the power of the purse belongs to Congress, and the administration lacked constitutional authority to transfer the military money toward the border project. Two Democratic appointees were in the majority; an appointee of President Donald Trump dissented.

“The President has long supported the construction of a border wall on the southern border between the United States and Mexico,” Chief Judge Sidney R. Thomas, an appointee of President Bill Clinton, wrote for the court in one of two decisions on the issue.

“Since the President took office in 2017, however, Congress has repeatedly declined to provide the amount of funding requested by the President.”

Whether the ruling will stand is uncertain. The Supreme Court last year blocked a 9th Circuit injunction that barred the administration from spending $2.5 billion of military money on the wall. The high court acted after the administration filed an emergency appeal.

Friday’s decisions reinstated the injunction, which the Trump administration is almost certain to appeal.

Brian Segee, a lawyer for the Center for Biological Diversity, had called the Supreme Court’s decision “an ominous signal” for the challengers of the wall. The center has a separate lawsuit pending against the administration’s use of military funding for the project.

The high court in July 2019 cleared the way for Mr. Trump to spend the money while the case was litigated in the 9th Circuit, a sign that a majority on the Supreme Court may overturn the 9th Circuit again. In a one -paragraph decision, the conservatives on the high court voted in favor of Mr. Trump, and the liberals dissented.

Mr. Trump argued the wall was needed to prevent drug smuggling.

But the 9th Circuit majority said Friday that the law allows for the transfer of Pentagon funds only for unanticipated military purposes, and a border wall “was not an unforeseen military requirement.” Drug smuggling at the border was neither a new nor an unforeseen problem, the majority said.

“There was no unanticipated crisis at the border,” Judge Thomas wrote, joined by Judge Kim McLane Wardlaw, also a Clinton appointee. “Nothing prevented

Congress from funding solutions to this problem through the ordinary appropriations process — Congress simply chose not to fund this particular solution.”

Judge Daniel P. Collins, a Trump appointee, said in a dissent that combating illegal drug activity was “plainly” a military function and argued the court should have upheld the money transfer.

The state of California and the Sierra Club, which were among those that filed the lawsuits, praised Friday’s decisions.

“Today, the court reminded the President — once again — that no one is above the law,” California Attorney General Xavier Becerra said in a statement.