Supreme Court justices were skeptical Monday of President Obama’s claim of almost unlimited appointment powers, saying he appeared to be trampling on the founders’ vision when he tried to do an end-run around the Senate in 2012.

While the justices appeared to struggle with how far to go in their ruling, most of them, including Mr. Obama’s nominees to the court, took dim views of the president’s move to name three members to the National Labor Relations Board in January 2012.

If they ruled narrowly, they could simply invalidate Mr. Obama’s appointments by finding he tried to make them when the Senate considered itself in session, not in recess. But the court also could go further and limit the president’s recess powers to the short period after the Senate adjourns at the end of each year.

In 90 minutes of oral arguments, the justices fought over whether the word “happen” means something different from what it did in the late 1700s, debated the separation of powers between the branches, and sparred with Donald B. Verrilli Jr., the Obama administration’s solicitor general, about the president’s expansive claims.

Mr. Verrilli said that whatever the language of the Constitution, Congress and the White House have come to a balance, with senators obstructing far more than they used to, and the president using his recess powers to circumvent them.