The Supreme Court on Thursday took a welcome step toward applying the rule of law to the Obama administration's assumption of extra-constitutional powers, but it was only a first step.

Many more are required.

In a unanimous decision, the court ruled that President Obama exceeded his legal powers when he appointed three members to the National Labor Relations Board in January 2011 while the Senate was not in recess under its own rules. At issue before the court was the president's power, under the Constitution, to make appointments without the consent of the Senate only when that body is in "recess." The president argued that the Senate was effectively in recess during a month of "pro-forma" meetings held every three days. Those meetings, he contended, were a sham designed expressly to prevent him from making appointments during the normal year-end suspension of legislative activity.

A majority of the court agreed, in an opinion by Justice Stephen Breyer, that the president had recess appointment power during such legislative holidays, but only provided they last at least 10 days. Justice Breyer based his opinion on an analysis of 200 years of history in the application of the recess appointment power. In doing so, he turned up such gems as the fact that the Senate traditionally does not consider Sunday a "day" for purposes of its calendar, and the attempt by President Theodore Roosevelt to exercise the recess appointment power during the infinitesimal time between the adjournment of one Senate session and the immediate commencement, on the same day, hour and minute of the next one.

Four other justices took an even stricter view of the limits on president appointment power, agreeing in a concurring opinion by Justice Antonin Scalia that it should be limited only to breaks between two-year Congresses, excluding so-called "intra-session" breaks, and should only apply to vacancies that occur during such narrowly defined recesses.

It is encouraging that all nine justices concluded that Mr. Obama had gone too far in making the three NLRB recess appointments even though they were later reconfirmed by the Senate following regular protocol.

On Wednesday, the court unanimously supported individual privacy rights in ruling that police must get a warrant to examine the contents of a suspect's cell phone. Both rulings are a welcome check on the excessive use of official authority.

The president's recess appointments to the NLRB first became controversial when its acting general counsel, Lafe Solomon, challenged Boeing's move to South Carolina, alleging that it was retaliatory to labor unions in Washington state. Though that spurious claim was dropped in 2011, it served to underscore the hazard of a recess appointment that would not have stood the advise and consent scrutiny of the Senate.

President Obama's other claims of executive power uncurbed by Congress have yet to be adjudicated. But on Wednesday House Speaker John Boehner announced he will ask the House to support legislation to bring suit in federal court to stop the president's "aggressive unilateralism" in modifying the requirements of laws on the books and selectively deciding which laws to enforce.

Mr. Boehner did not cite specifics in his charge that the president has failed to "faithfully execute" the nation's laws. But there is no shortage of examples of executive overreach in the many changes Mr. Obama has made to the Obamacare law without consulting Congress.

Even if the projected lawsuit fails to advance, Mr. Boehner has already made a valid and important point. The president has failed to respect the process of lawmaking or to adhere to the limits of his executive authority as set forth in the Constitution.

Left unchallenged, it can only weaken the checks and balances that are fundamental to our representative government.