Pushing toward the pinnacle of defensive hyperbole by proclaiming himself “a very stable genius” has done more than anything to subject Donald Trump to speculation at the Capitol about how psychologically fit he is for the presidency.

Trump’s first comprehensive medical exam on Friday after a year in office, when his sedentary lifestyle and junk food habits have only been enabled, did not dispel worries by many congressional gym rats about the 71-year-old’s ability to withstand the job’s bodily strain.

More and more of these conversations have veered into the largely unfamiliar territory of the 25th Amendment, which creates a mechanism for removing a president who is mentally or physically incapacitated.

But that system’s complexities, supermajority political thresholds and essential role for the vice president are designed to be a fail-safe against anything that might smack of a hostile Oval Office takeover.

Watch: David Hawkings’ Whiteboard — What’s the 25th Amendment?

As such, there’s next to no chance the amendment will get applied to the point where this Congress would play a part — at least given what’s currently known, or even conjectured, about Trump’s states of mind and body.

To be sure, 61 House members (all Democrats, including two-thirds of the party’s Judiciary Committee members) have signed on to a bill creating the sort of independent commission described in the 25th Amendment as one venue for determining a president’s capacity.

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And more than a dozen lawmakers, at least one of them a Republican, have met on the Hill in the past month with a forensic psychiatrist at Yale medical school, Bandy X. Lee, to hear her case that “Trump’s mental state poses a serious danger.”

In Politico last week, she detailed what she told lawmakers behind closed doors: “A few signs of this danger are: verbal aggressiveness, boasting about sexual assaults, inciting violence in others and the continual taunting of a hostile nation with nuclear weapons. Additional traits that are concerning are impulsiveness, recklessness, paranoia and rage reactions; a loose grip on reality with a poor understanding of consequences; a lack of empathy and belligerence toward others; and a constant need to demonstrate power.”

But that summation, which Lee declines to associate with a precise medical diagnosis because she’s never examined Trump, is a long way — medically, politically and constitutionally — from concluding the president is “unable to discharge the powers and duties of his office,” the threshold the 25th Amendment sets for replacing him either temporarily or indefinitely.

A rapid fix

The amendment sailed through Congress in just the first six months in 1965 and had been ratified by the necessary 38 states less than two year later — the rapid pace mainly a reaction to President John F. Kennedy’s assassination and the heightened tensions of the Cold War.

The new president, Lyndon B. Johnson, had a history of heart trouble, and the next two people in line, Speaker John W. McCormack of Massachusetts and fellow Democrat Carl Hayden of Arizona, the Senate president pro tem, were both ailing — and a combined 157 years old.

The amendment created a provision for filling a vice presidential opening for the first time, even though the post had been open 16 times when occupants died, resigned or ascended to the presidency. The system — a presidential nominee takes office upon confirmation by the House as well as the Senate — is how House Minority Leader Gerald R. Ford of Michigan got his promotion following Spiro Agnew’s resignation to face corruption charges in 1973, then how Gov. Nelson A. Rockefeller of New York got the job the next year when Richard Nixon resigned and Ford moved up.

The simplicity of that process stands in contrast to the amendment’s other half, addressing presidential incapacity.

It was hardly a theoretical problem back then. James A. Garfield lingered for 80 days after being shot before dying, for example, while Woodrow Wilson was incapacitated by strokes with 17 months left in his term and Dwight D. Eisenhower suffered both a heart attack and a stroke.

In these and other cases, power was never even informally transferred because none of the vice presidents wanted to seem like usurpers.

Now, the Constitution has two procedures for transferring authority.

In the first, a president temporarily transfers power to the vice president. Ronald Reagan and George W. Bush both did so before anesthesia for medical procedures.

In the second, a president is unable to fulfill his constitutional role but cannot make the decision to step aside, probably because of a severe physical disability, or else refuses to yield power, probably because of significant mental health problems.

In that case, the vice president becomes “acting” president when he decides the time is appropriate and also obtains sign-off from either a majority of the Cabinet or some other panel created by Congress to take decision-making away from the department heads.

This is the commission, of physicians and former top administration officials, that would be established under the House bill — which, of course, is going nowhere unless plenty of Trump’s fellow Republicans conclude it’s necessary. (And even then, he could veto the measure.)

Undefined language

If the president pronounces himself ready to get back to work, the vice president and his fellow deciders (the Cabinet or the commission) would have four days to disagree and stop him.

At that point, Congress would have the final word. It would have three weeks to settle the dispute but could countermand the president’s judgment only with two-thirds majorities in both the House and Senate.

For all those elaborate and precise mechanics, though, the amendment’s text is silent on how “unable,” “inability” or “disability” should be defined.

The congressional authors decided to leave the language deliberately vague. Some were concerned a precise definition might be made obsolete by changes in the world of medicine. Others wanted to make sure that the elected officials given the decision-making powers had wide latitude to make what is ultimately a political decision.

Still, the debate made clear Congress didn’t want the 25th Amendment to be a tool for combating a president’s incompetence, laziness, unpopularity or even impeachable conduct.

They talked about invoking the involuntarily removal mechanisms only when a president was clearly and unequivocally incapacitated — in a coma, near death or in severe psychological distress.

The vice president, the Cabinet or the special panel should get involved when the president does “not possess the mental capacity to make a decision and perform the powers and duties of his office,” Democrat Birch Bayh of Indiana, the principal author of the amendment, said during the Senate debate in June 1965.

“We are not getting into a position, through the pending measure, in which when a president makes an unpopular decision, he would immediately be rendered unable to perform the duties of his office,” he said.

In other words, no one should expect these powers to get used, especially for the first time, in a way that could be portrayed by history as a constitutional crisis culminating in a coup.

A presumably politically loyal vice president would be the essential actor in any initial invoking of this extraordinary provision. And, in the end, it would take bipartisan supermajorities in Congress to move the president aside. It’s hard to imagine any of that happening under Vice President Mike Pence and the current GOP control on the Hill.