During Wednesday’s press conference, US President Donald Trump threatened to use a little-known constitutional provision to force Congress to adjourn so he could then make recess appointments to the Cabinet and judiciary.

The president spoke of the many vacancies both in executive agencies and on the federal bench and complained of “partisan obstruction” preventing nominees from receiving hearings in the Senate. He singled out the practice of pro forma sessions, which is when both houses of Congress, while they are in recess, hold brief parliamentary sessions precisely so that neither chamber is ever officially adjourned. This is a long-standing Congressional practice in order to prevent presidential recess appointments that bypass the Senate confirmation process.

Article II, Section 3 of the US Constitution gives the president power to convene either or both chambers of Congress “on extraordinary occasions,” as well as the power to “adjourn them to such time as he shall think proper,” but only “in case of disagreement between them, with respect to the time of adjournment.” While presidents have called extraordinary sessions of Congress, no president has ever used the power to force Congress to adjourn.

Trump could only invoke the power if there is a disagreement between the House and Senate regarding adjournment, which currently there is not. A spokesperson for Republican Senate Majority Leader Mitch McConnell said following the briefing that the senator had been in touch with the White House and “shared [the president’s] continued frustration with the process,” but also that “under Senate rules [he] will take consent from [Democratic Minority] Leader Schumer.” The statement suggested that McConnell will continue to hold pro forma sessions in the Senate, despite the president’s frustrations.