“For purposes of the Recess Appointments Clause, the Senate is in session when it says that it is, provided that, under its own rules, it retains the capacity to transact Senate business,” the court ruled in the case of NLRB v. Noel Canning. “This standard is consistent with the Constitution’s broad delegation of authority to the Senate to determine how and when to conduct its business, as recognized by this Court’s precedents.”

The court ruled that if the Senate is not able to conduct business under the rules, it would be in recess for the purposes of the recess appointment power. But it noted that during the pro-forma sessions in question, the Senate is able to — and indeed has — passed legislation via unanimous consent requests.

Senate Republicans helped lead the opposition to the Obama administration’s reading of the appointment power, being represented at oral arguments by Miguel Estrada.

“The President made an unprecedented power grab by placing political allies at a powerful federal agency while the Senate was meeting regularly and without even bothering to wait for its advice and consent. A unanimous Supreme Court has rejected this brazen power-grab,” Senate Minority Leader Mitch McConnell, R-Ky., said in a statement lauding the ruling. “All Americans should be grateful for the Court’s rebuke of the administration—and the Democratic Majority in the Senate should be embarrassed by its failure, yet again, to stand up to the President and to defend the Senate’s uniquely important role under our Constitution. I was proud to lead the effort to defend the Senate against the President’s unprecedented power grab.”

Sen. Orrin G. Hatch, a former Republican chairman of the Judiciary Committee, said in a statement the ruling would strengthen efforts on separation of powers issues.

“Today, the Supreme Court emphatically rejected President Obama’s brazen efforts to circumvent the Constitution, bypass the people’s elected representatives, and govern above the law. The Court’s unanimous decision demonstrates how the President’s actions contradicted both constitutional text and longstanding precedents that enshrine the Senate’s legitimate role in federal appointments. The Court has reaffirmed the Senate’s vital advice-and-consent role as a check on executive abuses,” the Utah Republican said.

Justice Stephen Breyer delivered the opinion, deciding the case on the more narrow question than the conservative justices led by Antonin Scalia. In the concurrence, Scalia argued against a broader swath of intra-session recess appointments. That had been the view of several federal appeals courts.

But, the fact that the court was unified on the underlying question should come as no surprise. Republican senators left the oral arguments confident that they would prevail, and the questioning from justices nominated by both Democratic and Republican presidents, including Obama himself, cast doubt on the administration case.

Senate Democrats sat on the sidelines as the case went through the legal process, and on Thursday, Majority Leader Harry Reid of Nevada said that Obama was right to make the dubious appointments to the NLRB. He went further to say that helped make the case for using the so-called nuclear option to change the rules in November to prevent the minority from blocking nominations.

“More than anything, today’s Supreme Court ruling underscores the importance of the rules reform Senate Democrats enacted last November. Without that reform and with today’s ruling, a small but vocal minority would have more power than ever to block qualified nominees from getting a simple up-or-down vote on the floor,” Reid said in a statement. “Since the November reform the Senate has been confirming qualified nominees at a steady pace and today’s ruling will have no effect on our ability to continue ensuring that qualified nominees receive an up-or-down vote.”

The decision also makes the midterm elections even more important. If McConnell ascends to majority leader, he will have the power to block Obama’s nominations by staying in pro forma sessions.