What is the 25th Amendment of the US Constitution and can it be used to remove Donald Trump from office?

Donald Trump’s freewheeling speech in Phoenix – during which he rounded on the media, attacked critics on his own side and threatened to shut down the government – provoked alarm among viewers of all political hues.

James Clapper, the former Director of National Intelligence, told CNN: “I really question his ability to be — his fitness to be — in this office.

“I also am beginning to wonder about his motivation for it — maybe he is looking for a way out.”

Not for the first time in this presidency, Americans are questioning whether Mr Trump is mentally competent to hold office.

During the speech, internet searches for the 25th Amendment spiked as part of a fresh debate about whether it could be used to remove Mr Trump from office.

What is the 25th Amendment?

It was instituted after the death of John F Kennedy, providing a formal mechanism by which the Vice-President could take power if the president dies, resigns, or is removed from office. It also allows for the Vice-President to take over temporarily if the president cannot fulfill his or her duties, such as when President George W Bush went under general anaesthetic for two colonoscopies. Dick Cheney took over on each of those occasions.

How can a president be removed from office?

This comes in section four, which states: "Whenever the Vice President and a majority of either the principal officers of the executive departments or of such other body as Congress may by law provide, transmit to the President pro tempore of the Senate and the Speaker of the House of Representatives their written declaration that the President is unable to discharge the powers and duties of his office, the Vice President shall immediately assume the powers and duties of the office as Acting President.”

In practice what that means is Mike Pence plus 13 of Mr Trump’s 24 cabinet members would have to agree.

On what grounds might a president be removed?

The amendment is vague about the specifics. However, John D Feerick, former dean of Fordham Law School who served as one of its architects, said Senators who signed the amendment into law were clear it must be based on "reliable facts regarding the president's physical or mental faculties," not personal prejudice.

"If you read the debates, it's also clear that policy and political differences are not included, unpopularity is not included, poor judgment, incompetence, laziness, or impeachable conduct — none of that, you'll find in the debates in the congressional record, is intended to be covered by Section IV," he told Business Insider.

What if the president refuses?

The mechanism was designed for a president who was incapacitated, not for one willing to fight back.

He or she is protected by a safeguard. Within 21 days of being triggered, the amendment requires two-thirds of both houses to uphold the decision. If they don’t then power reverts to the president.

How likely is it that the 25th amendment could be used to remove Mr Trump?

Very unlikely. It requires both Mr Pence and a majority of the cabinet to agree to oust the president. If he were not physically or mentally incapacitated – through ill health, a stroke or some such - it would effectively amount to a palace coup.

In other words, Mr Trump’s very closest allies are the ones to make the decision.

Any number of Democrats, TV pundits and armchair psychiatrists can label Mr Trump as unfit for office but it makes not one scrap of difference.

Just like impeachment, the tables are tilted to make it very difficult to remove a sitting president from power.