A three-judge panel in the Ninth Circuit Court of Appeals unanimously upheld a lower court’s order blocking the Trump administration from enforcing its immigration and refugee order, handing the president his highest-profile legal defeat yet over the controversial ban.

In an unsigned opinion, the panel decisively rejected the Justice Department’s arguments against the restraining order. “We hold that the Government has not shown a likelihood of success on the merits of its appeal, nor has it shown that failure to enter a stay would cause irreparable injury, and we therefore deny its emergency motion for a stay,” the three judges wrote in their 29-page decision.

President Trump responded to the ruling with a cryptic, two-line message on Twitter.

While much of the discussion centered around the ban’s constitutionality, the judges largely sidestepped its legal and constitutional merits. Instead, the panel’s ruling focused on whether Judge Robart’s temporary restraining order, which blocked the federal government from enforcing key parts of the executive order while legal proceedings continue, was justified.

The case, Washington v. Trump, is the most prominent lawsuit challenging Trump’s immigration and refugee order. Among other provisions, the order temporarily suspended the U.S. Refugee Admissions Program for 120 days, barred Syrian refugees from admission until further notice, and suspended immigrant and non-immigrant visa travel from seven Muslim-majority countries for 90 days. The visa suspensions went into effect immediately, causing chaos at major U.S. airports as some travelers found themselves unable to enter the country while in transit.

The Trump administration defended its order on national-security grounds, saying it was necessary while it conducts a comprehensive review of the nation’s security procedures at the border. But that argument won little sympathy among the three judges, who noted the lack of proof offered by Justice Department lawyers during oral arguments on Wednesday.

“The Government has pointed to no evidence that any alien from any of the countries named in the Order has perpetrated a terrorist attack in the United States,” the panel wrote. “Rather than present evidence to explain the need for the Executive Order, the Government has taken the position that we must not review its decision at all.”

“We disagree,” they added.

Bringing the lawsuit were the Democratic attorneys-general of Washington state and Minnesota. In their brief, the two officials claimed the executive order would hurt both states’ economies and tax bases by disrupting the ability of their noncitizen immigrants to travel. They also argued the order violated the First Amendment’s religious-freedom protections and the Fourteenth Amendment’s equal-protection guarantee by targeting Muslims.

While the judges did not rule on the merits of those arguments, they did hand the states a crucial procedural victory by ruling they had standing to bring the lawsuit against the federal government. To have standing in a lawsuit, the litigants—in this case, the states—must prove they have a direct stake in its outcome. The panel pointed to the order’s impact on both states’ higher-education systems, ruling that the disruptions for foreign-born students and faculty justified the intervention.

“This is a complete victory for the state of Washington,” Washington Attorney General Bob Ferguson said during a press conference. “We are a nation of laws, and as we have said from day one, those laws apply to everyone in the country. That includes the president of the United States.”

Justice Department lawyers strongly defended the order as a proper use of the president’s broad authority on immigration. The Trump administration frequently pointed to a section of the U.S. Code that authorizes the president to “suspend the entry of all aliens or any class of aliens as immigrants or nonimmigrants” if he deems their entry “detrimental to the interests of the United States.” The administration also cited the traditionally wide latitude given by the courts to the president and Congress to craft and enforce the nation’s immigration laws. But the judges declined to exercise that discretion, citing past judicial interventions into national-security matters.

“The Government indeed asserts that it violates separation of powers for the judiciary to entertain a constitutional challenge to executive actions such as this one,” they wrote. “There is no precedent to support this claimed unreviewability, which runs contrary to the fundamental structure of our constitutional democracy.”

Judge James Robart, who was nominated by President George W. Bush in 2004, issued the temporary restraining order on Friday to block the ban’s enforcement nationwide pending further hearings. Robart is one of several federal judges who has blocked parts of the executive order since its announcement on January 27. But his temporary injunction was the most sweeping one yet issued by a judge, effectively negating the order’s core functions. The following day, the State Department and Department of Homeland Security said they would abide by the judge’s order and roll back their enforcement of the ban.

That drew criticism from Trump, who railed against Robart’s legitimacy in a series of posts on Twitter last weekend. “The opinion of this so-called judge, which essentially takes law-enforcement away from our country, is ridiculous and will be overturned!” Trump wrote on Saturday. He continued that criticism throughout the week, complaining that the courts were “so political” and claiming that even a “bad high school student” would rule in his favor. The remarks drew an unusual rebuke from federal judge Neil Gorsuch, Trump’s nominee for the vacancy on the U.S. Supreme Court, who called them “disheartening” and bad for the federal judiciary’s morale.

Thursday’s ruling is not the end of the legal saga. The Trump administration’s next move would be an appeal to the Supreme Court. If the Court deadlocks in a 4-4 vote on whether or not to uphold Robart’s temporary restraining order, the Ninth Circuit’s decision will stand. Both parties will also return to the federal district court in Seattle, where Robart will next consider a full injunction against enforcing the executive order for the duration of the trial.