President Trump threatened Wednesday to try to force Congress to adjourn so he could fill his administration’s vacancies without Senate approval, the second time this week he has claimed unprecedented executive authority amid the coronavirus pandemic.

The president cited a never-exercised constitutional power to shut down Congress if the House and Senate are in disagreement over adjourning, pushing both the executive and legislative branches into uncharted territory.

On Monday, Trump had asserted that he had “total” authority over the decision to reopen the country, overruling governors intent on protecting public health and containing further spread of the coronavirus. He seemed to backtrack Tuesday, suggesting he would work with the governors on such a step.

At his daily coronavirus task force briefing Wednesday, Trump slammed the common practice by the House and Senate to hold pro forma sessions every two or three days but never formally adjourn, thwarting Trump’s ability to bypass the regular Senate confirmation process and install nominees by recess appointments.

“The current practice of leaving town while conducting phony pro forma sessions is a dereliction of duty that the American people cannot afford during this crisis,” Trump told reporters.

Article II, Section 3 of the Constitution says the president “may, on extraordinary Occasions, convene both Houses, or either of them, and in Case of Disagreement between them, with Respect to the Time of Adjournment, he may adjourn them to such Time as he shall think proper.”

Senate Majority Leader Mitch McConnell (R-Ky.) spoke to Trump on Wednesday but signaled that he wasn’t on board with the president’s plan. Any attempt to formally adjourn the Senate would require all 100 senators traveling back to Washington for such a vote — which McConnell and Senate leaders have deemed unsafe at this point.

If such a resolution passed in the Senate, Speaker Nancy Pelosi (D-Calif.) would have to bring the current 429 House members back to vote on the measure. The Democratic-led chamber likely would oppose it, creating the disagreement between the two chambers.

The House and Senate have been holding pro forma sessions since lawmakers left Washington at the end of March. The Senate held a session Thursday afternoon and scheduled four more throughout the month.

In a statement Wednesday, a McConnell spokesman indicated he would operate under Senate rules and work with Democrats.

“The leader pledged to find ways to confirm nominees considered mission-critical to the covid-19 pandemic, but under Senate rules that will take consent from Leader Schumer,” said a McConnell spokesman, referring to Senate Minority Leader Charles E. Schumer (D-N.Y.).

McConnell had no comment Thursday when reporters asked him about Trump’s criticism of pro forma sessions.

Controversial nominations can require days of valuable Senate floor time to process, and with Democrats opposing scores of Trump nominees, McConnell has prioritized confirming lifetime appointments to the federal judiciary. That has meant some nominees to sub-Cabinet posts, commissions and other posts have languished.

Trump claimed he needed to fill jobs in his administration to deal with the public health emergency, complaining that Senate Democrats blocked his nominations, even though most of the vacancies in the federal government are because Trump hasn’t selected anyone to fill them. Several of the ones he has nominated haven’t had a confirmation hearing yet in the GOP-led Senate, including Rep. John Ratcliffe (R-Tex.), the nominee for director of national intelligence. Trump mentioned Ratcliffe as an example of someone he wanted quickly confirmed.

Rep. Justin Amash (I-Mich.) quickly tweeted that Trump could not take such a step if the House did not vote to adjourn, writing: “Without one chamber participating in this improper scheme, this action would be unconstitutional. The president has no general, unilateral power to adjourn Congress. He may do so only in the limited ‘Case of Disagreement between them, with Respect to the Time of Adjournment.’ ”

Rep. Jamie Raskin (D-Md.), a member of the House Judiciary Committee who taught constitutional law, said Trump’s idea of “dissolving an assembly comes out of a dictator’s handbook. That’s banana republic stuff.”

Raskin said no other president has “has tried to force a collision between the House and the Senate to try and indefinitely adjourn one of the houses. . . . That would provoke a true constitutional crisis. The president has just never reconciled himself to the existence of other branches” of government.

Trump suggested that the courts would have the final say.

“They know they’ve been warned and they’ve been warned right now. If they don’t approve it, then we’re going to go this route and we’ll probably be challenged in court and we’ll see who wins,” Trump said when asked if there was a timeline on his threat.

In fact, in 2014, the Supreme Court sided with Senate Republicans in a dispute with President Barack Obama over a recess appointment to the National Labor Relations Board.

The court ruled unanimously that Obama exceeded his constitutional authority in making high-level government appointments in 2012 when he declared the Senate to be in recess and unable to act on the nominations.

“The Senate is in session when it says it is,” Justice Stephen G. Breyer wrote for the court.

McConnell, then the Senate minority leader, hailed the ruling.

“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,” McConnell said.

On Wednesday, House Speaker Nancy Pelosi (D-Calif.) did not respond to request for comment. Neither did Schumer, nor House Minority Leader Kevin McCarthy (R-Calif.).

Steve Vladeck, a professor at the University of Texas School of Law, dismissed Trump’s comments as an empty threat.

“Leaving aside that he probably *can’t* do this (because it’s unlikely the chambers will disagree), he‘s not actually going to send Congress home — foreclosing any additional relief legislation — in the middle of a national public health and economic crisis with elections in November,” Vladeck tweeted.

Republicans and Democrats had rejected Trump’s assertion earlier in the week that he had the authority to order states to lift their safety measures.

Paul Kane and Erica Werner contributed to this report.