President Donald Trump on Wednesday threatened to adjourn both chambers of the US Congress - the Senate and the House of Representatives - in an effort to pressure Senate Republicans to confirm his nominees more quickly.

The comments came during one of Trump's daily coronavirus briefings and caused puzzlement - even some alarm - because his authority to convene or adjourn Congress is obscure. Indeed, the authority has been discussed but never used before.

"Perhaps it's never been done before, nobody's even sure if it has, but we're going to do it," Trump said at his briefing. "We'll probably be challenged in court, and we'll see who wins."

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Here's what's going on.

All presidential appointments to top executive branch positions must be approved by the Senate. But Article II of the Constitution provides that a president may make executive appointments directly without Senate approval when the Senate is in recess.

During the presidency of Democrat Barack Obama, however, Senate Republicans deployed a parliamentary manoeuvre to block Obama's recess appointments by taking their breaks as scheduled but coming into so-called "pro forma" session every third day to, technically, keep the body in session. The practice continues today under the Republican majority.

Party deputies remain in Washington, DC, to handle these pro forma sessions while other members return to their states. Little to no actual business is done.

Trump called the manoeuvre "a dereliction of duty that the American people cannot afford during this crisis".

US President Donald Trump reacts to a question during the daily coronavirus taskforce briefing at the White House in Washington, DC [File: Joshua Roberts/Reuters]

Trump is frustrated because he has nominated 82 people to fill vacant executive branch positions who have not yet been approved by the Senate, and with Congress in recess, nothing is happening.

"No President in history has ever used the Constitutional power to adjourn Congress," US presidential historian Michael Beschloss said on Thursday in a tweet.

Former presidents Woodrow Wilson, Howard Taft and Franklin Roosevelt all were urged at one point to adjourn Congress and all refused, Beschloss said.

But his power to do so is there in black and white. 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".

Despite that language, practically speaking, it would be virtually impossible for Trump to exercise that right.

Rules and practice of the Senate and House would require the Senate to take up and approve a resolution of adjournment. Before that resolution is even voted on, a so-called "cloture vote" to end debate would likely be required. Cloture votes require a 60-vote majority of the 100 sitting senators, to pass. Republicans, who hold 53 seats, would need at least seven Democrats (or independents) to join them in the cloture vote.

Then, the measure would need to be approved by a vote of the House of Representatives, which is solidly in the hands of Democrats. Highly unlikely, given the animosity between Trump and House Speaker Nancy Pelosi.

In any case, the Senate and House already have an effective agreement on an adjournment date - January 3, 2021, which falls after the November election but before the inauguration of the next president. To change the date, the Senate and the House would each have to approve new, different adjournment dates through that convoluted process. If the dates they suggest differ - the "Case of Disagreement between them, with Respect to the Time of Adjournment" mentioned in the Constitution - Trump could conceivably step in and adjourn Congress.

The bottom line is that neither Pelosi nor Senate Republican Majority Leader Mitch McConnell, despite being a staunch supporter of the president, have signalled interest in going down the road mapped out above. Trump is effectively sidelined on the matter.

"This power has never been used and should not be used now," tweeted Jonathan Turley, a constitutional law professor at George Washington University who supported Trump during the House impeachment proceedings last year.

Senators of both parties should vote to support the congressional control over adjournment. Absent a "disagreement" there is no presidential power to adjourn under Article II. A pandemic should not be an invitation for pandemonium. Indeed, we need regular order now more than ever — Jonathan Turley (@JonathanTurley) April 15, 2020

Democratic presidential candidate Joe Biden, appearing on a TV talk show on Thursday, disparaged Trump's claim to be able to adjourn Congress along with prior comments that he has "absolute authority" to tell governors when to reopen their states.

"I don't get it. It seems to always be about him. Everything is about him," Biden said on MSNBC. "This is not about him. It's about us. It's about the American people."

"It is one of these things that I don't understand. I mean, in the way he goes in and attacks the press and the things he says, like he's going to adjourn the Congress, he has absolute authority. It's like something out of a really bad play," Biden said.