Republican senators left the Supreme Court on Monday optimistic that the justices would rule that President Barack Obama ran afoul of the Constitution in making recess appointments to the National Labor Relations Board.

The Supreme Court heard oral arguments in the matter of NLRB v. Noel Canning, which questions the validity of recess appointments made by Obama during a time when the Senate was at least ostensibly in session, gaveling in and out every three days. Several GOP senators were in town early for the arguments, including Minority Leader Mitch McConnell of Kentucky. McConnell’s campaign has also promoted the legal effort.

While the Supreme Court can be difficult to read based on questions during oral argument, there seemed to be support among justices for the idea that the Senate may determine what constitutes a “session” and a “recess.”

Sen. Mike Lee’s reading of the tea leaves of the justices predicts an overwhelming rebuke to the executive branch.

“I expect that the court will affirm the judgment entered by the D.C. Circuit” against the appointments, the Utah Republican said. “The solicitor general’s arguments were not, in my opinion, well received.”

Speaking to reporters outside the court, Lee said he had the sense that “most, perhaps all, of the justices understand, appreciate and respect the fact that the Senate does have the power … to establish its own rules and procedure, to decide things like when it’s in session and when it isn’t.”

The D.C. Circuit went beyond just ruling that the pro forma Senate sessions invalidated the disputed appointments, saying that only vacancies that arise during a recess between sessions of Congress qualify for such appointments. The justices did seem to have more questions about the effects of such a sweeping decision.

“I do think it will be a closer question as to whether they get to … the issue regarding when the vacancy happened,” Lee said. “It was less clear to me that that one was going to be a lopsided victory for respondents. That one could end up being a closer call. Perhaps the basis of a 5-4 or 6-3 decision.”

In addition to Solicitor General Donald Verrilli Jr. representing the government and counsel for the canning company that challenged the NLRB’s authority to make decisions with a quorum that included the questionable appointees, Miguel Estrada represented the interests of McConnell and other Senate Republicans.

“I thought Miguel Estrada did a fabulous job. I thought he was superior in his arguments,” said Alabama GOP Sen. Jeff Sessions, recalling Estrada’s own confirmation battle to the D.C. Circuit during the George W. Bush administration, a nomination derailed by Democrats making use of filibuster rules that no longer apply to such nominations thanks to the use of the “nuclear option” by Senate Majority Leader Harry Reid and his caucus.

Sessions argued Monday that Reid should have taken action against Obama’s NLRB appointees, as well.

“He was more moved by the short-term political gain of getting the appointments than he was to defend the integrity of the Senate, and for that he should get bad marks historically,” Sessions said. “There’s no doubt about it.”

Sessions also said it was ironic that Reid had started the pro forma session routine during the Bush administration.