25th Amendment: What it is and how it works, according to a constitutional law expert

On Thursday, officials from House Speaker Nancy Pelosi and Senate Democratic Leader Chuck Schumer to at least one Republican, Rep. Adam Kinzinger, called for the invocation of the 25th Amendment, Section 4, to remove President Trump from office before his term ends on Jan. 20. It comes in the wake of the deadly pro-Trump riot by on Wednesday in Washington, D.C.

So what is the 25th Amendment and its Section 4 provision? Here information about the amendment and whether Section 4 could be used against Trump in this situation.

The 25th Amendment was passed by Congress on July 6, 1965 and ratified on Feb. 10, 1967. The amendment has four sections that provide avenues by which a sitting U.S. president may be removed (temporarily or permanently) from the helm of the government, if the president is not able (physically or mentally) to perform the duties of the office.

The 25th Amendment has been used multiple times over the years, according to Richard Kay, an expert on constitutional law and a Wallace Stevens Professor of Law Emeritus from the University of Connecticut.

Most recently, it was used in 2007 when then-President George W. Bush appointed his Vice President Dick Cheney as acting president for the time period Bush was under general anesthesia during a colonoscopy. In that instance, Section 3 was used, which allows the president to willingly discharge his powers.

However, Section 4 has never been used.

For the 25th Amendment, what “the drafters had in mind was the president being in some way physically disabled,” Kay tells CNBC Make It. “But they throw this one at the end (Section 4), which clearly contemplates some kind of situation where the powers that be think the president is incapable of going on and the president disagrees,” he says.

It comes into play when the vice president and certain other officials declare that the president is “unable to discharge the powers and duties of his office,” the section says, but does not require the president’s cooperation.

“It’s a way in which people who work with the president and are convinced that the president cannot effectively carry out his functions, are able to at least temporarily displace him and get the vice president to take over,” Kay says.

The most important factor needed to use the 25th Amendment is having the vice president and a majority of the cabinet on board, says Kay.

“If the vice president and a majority of the cabinet send a letter to the speaker of the house and the president pro tempore of the Senate saying that, in their opinion, the president is incapable of [the] carrying out of his functions and duties…instantly, the president ceases to have authority and the vice president takes over,” Kay says.

However, should that happen, the president can immediately follow up with his own letter to congressional leaders saying that he is indeed capable of carrying out his responsibilities.

“At that point, the president is back in charge,” Kay says.

The vice president and cabinet officers could then send a final letter to Congress disputing the president’s claim and restating that the president is unable to do to job, Kay says.

After that, according to Constitution, it’s up to the houses of Congress to decide and vote on the matter, and they have up to 21 days to do so, Kay says. During the voting process in Congress, the vice president would be in charge.

While the process sounds complicated, “these communications can go lickity split in a situation like this,” Kay says.

Displacing the president would require an affirmative vote of two-thirds of the members of each House.