The anonymous op-ed in the New York Times said that senior staff officials have considered invoking the 25th Amendment to have President Donald Trump declared incapable of performing the duties of office. This would be unprecedented in American history.

At this point, it is highly unlikely to be used, but it is stunning that it has been discussed in the White House at all.

The 25th Amendment was adopted in 1967, primarily to clarify presidential succession. The Constitution says very little about what happens when a president leaves office in the middle of a term. In 1841, President William Henry Harrison died in office and it was unclear whether Vice President John Tyler was the acting president or was to assume the duties of president. Tyler chose the latter approach, but this was highly disputed.

Section 1 of the 25th Amendment finally resolved this by stating: “In case of the removal of the President from office or of his death or resignation, the Vice President shall become President.”

Prior to 1967, the office of vice president had been vacant 16 times due to the death or resignation of the vice president or his succession to the presidency. Section 2 of the 25th Amendment also addressed this: “Whenever there is a vacancy in the office of the Vice President, the President shall nominate a Vice President who shall take office upon confirmation by a majority vote of both Houses of Congress.”

After Vice President Spiro Agnew resigned in 1973, President Richard Nixon nominated House Speaker Gerald Ford to be vice president. Less than a year later, Nixon resigned and Ford became president. Ford then nominated Nelson Rockefeller to be his vice president.

Before the 25th Amendment, the Constitution also did not address the president becoming temporarily incapacitated.

Section 3 provides: “Whenever the President transmits to the President pro tempore of the Senate and the Speaker of the House of Representatives his written declaration that he is unable to discharge the powers and duties of his office, and until he transmits to them a written declaration to the contrary, such powers and duties shall be discharged by the Vice President as Acting President.” Section 3 has been invoked a few times,including when some presidents have had minor surgical procedures.

But the focus now is on Section 4, which creates a procedure for removing a president who is incapable of doing the job — and which has never been used. The vice president and a majority of the Cabinet would need to offer a written declaration “that the President is unable to discharge the powers and duties of his office.”

The vice president then immediately becomes the acting president. But the president can respond with a written declaration that he is able to perform the job and reassume the office. If they choose, the vice president and the majority of the cabinet can take the issue to Congress, where it takes a two-thirds vote of both the House and Senate to deem the president unfit.

The Constitution offers no criteria for deciding when the president is unable to discharge the powers and duties of the office. Ultimately, it is left to the Cabinet and to Congress.

Although the reports of theTrump White House are remarkably consistent and deeply dismaying, it isdifficult to say that Trump is “unable to discharge the powers and duties ofthe office.” While he demonstrates a startling lack of understanding of theConstitution and his behavior is unlike that of any president in history, thatdoes not make him unable to perform the duties of the office.

Perhaps there will be revelations from special counsel Robert Mueller of significant criminal liability for Trump. Or maybe it will turnout that Russia really does have information to compromise Trump. Or maybe his behavior will become even more erratic.

But at this stage, there isn’t sufficient evidence to say that he is unable to discharge the powers and duties of the office. Most of all, it seems highly unlikely that the vice president,a majority of Trump’s Cabinet and, ultimately, two-thirds of both houses of Congress would vote to declare Trump to be incompetent and remove him from office.

Erwin Chemerinsky is dean and professor of law at the UC Berkeley School of Law.