Republican U.S. presidential nominee Donald Trump speaks during the first debate with Democratic U.S. presidential nominee Hillary Clinton at Hofstra University in Hempstead, New York, U.S., September 26, 2016. REUTERS/Lucas Jackson

One of this campaign's most unnerving aspects is that Donald Trump's perpetual biliousness has numbed us to the mania fueling his vulgarity. But last week those not yet insensate could absorb an appalling reality: the presidential candidate of a major party was focused on accusing Miss Universe 1996 -- falsely -- of making a porn film. This singular digression marked the moment when Trump retroactively turned a bad debate into a calamity, warning us yet again of his pervasive instability.

In itself, the reason for his poor performance exposed his mental and emotional unfitness to lead. Faced with the most important moment in his political life -- the chance to persuade his fellow Americans to entrust him with the presidency -- Trump prepared by doing almost nothing. Aides charged with prepping him privately revealed that he was unwilling, perhaps unable, to pay attention.

This is a stunning incapacity: a failure to summon, or even to appreciate, the seriousness of mind and spirit required of a leader at such a public crossroads -- suggesting that there is nothing, ever, which can penetrate Trump's surreal self-absorption. But as revealing of his psychological deficiencies was his aides' apparent inability, even in the wake of his miserable showing, to suggest ways in which he could improve.

Trump, it emerged, insisted that he had beaten Hillary Clinton and would not hear otherwise. Unable to advise him, his minions were reduced to communicating with their leader through leaks to the press, stressing his need for preparation before the next debate. A man who cannot absorb the reality which surrounds him, and renders his advisors fearful of addressing it, is frightening to contemplate as president.

For Trump, the reality of the first debate was devastating. His defeat on Monday night did not stem from a gaffe, or one bad answer. Rather, so comprehensive was his failure in both substance and style that presidential historians could not find its equal.

Ninety minutes of exposure revealed that he has little grasp of -- or interest in -- the subject matter of the presidency itself. Instead the subject which absorbed him was... himself. And Trump as he conceives himself is superior to those those other humans for whom, individually, he shows no more regard than he does for society at large.

He was, as ever, self-referential, whiny and defensive, blaming others for his problems, whether with individuals or the IRS. Baited by Clinton, the hereditarily wealthy Trump recast himself as a self-made billionaire, and offered such practices as profiting from the 2008 housing collapse, employing multiple bankruptcies, and paying no income tax as evidence of his savvy. As for habitually stiffing contractors, by Trump's solipsistic account their work was habitually sub-standard.

Widely perceived as a chronic liar, he lied still more -- often and detectably. This was particularly damaging with respect to accusations of misogyny: instead of expressing regret about past slurs against women, he denied uttering them at all. And, in the end, it was his sexism which greased the skids of his self-destruction.

Here, too, he should have been prepared -- surely by now someone, perhaps Kellyanne Conway, has revealed to Trump that millions of Americans deem him hostile to women. Indeed, before the debate Alexandra Petri of the Washington Post tweeted, "Finally, the whole country will watch as a woman stands politely listening to a loud man's bad ideas about the field she spent her life in."

A lesser man would have taken the hint. Instead, Trump interrupted Clinton constantly and, with his own endurance and concentration clearly flagging, chose to deride her stamina. While Trump may not have been prepared, Clinton was.

After reprising Trump's insults to women, Clinton went for the jugular: "And one of the worst things he said was about a woman in a beauty pageant... [H]e called this woman 'Miss Piggy.' Then he called her 'Miss Housekeeping,' because she was Latina. Donald, she has a name. Her name is Alicia Machado." As Trump interrupted yet again, Clinton finished, "She has become a U.S. citizen, and you can bet she's going to vote this November."

A grim moment, made worse when Trump defended himself by gratuitously offering that Rosie O'Donnell, previously unmentioned, "deserves" his prior insults. But no one -- except, perhaps, the Clinton campaign -- could imagine what Trump would do next. Liberated from his handlers, he turned his "Machado moment" into an attenuated display of his profound emotional disturbance, kicking off the most disastrous and disturbing week a modern presidential candidate has ever inflicted on himself.

The subject dated back to 1996, when Trump ran the Miss Universe contest -- and was potentially incendiary. In an earlier interview, Machado asserted that Trump's psychological abuse about her weight contributed to her anorexia and bulimia, a claim she repeated on camera after the debate. A normal man would grasp the number of women who, repelled by body shaming, would find this assertion sympathetic.

Worse for Trump, the abuse itself was captured by a scarifying video -- for once, he could not lie about his conduct. In a series of excruciating filmic moments, Trump shepherded the teenaged Machado to a gym, where she exercised in front of dozens reporters and cameramen. Trump himself provided the color commentary."This is someone who likes to eat," he informed his audience, adding that, "the way she's going, she'd eat a whole gymnasium."

Quite obviously, a sane candidate would leave this toxic incident behind or, better, find a way to apologize. Not Trump. The Tuesday morning after the debate, he took to Fox News to belittle Machado and defend his disparagement of her appearance. "She was the winner and she gained a massive amount of weight,and it was a real problem. Not only that -- her attitude. And we had a real problem with her."

No doubt to his surprise, commentators and much of the public reacted with revulsion and even shock: Trump was echoing his prior attack on individuals like Judge Curiel and the Khans, this time in a way which, perhaps, was even more unseemly. But with the deranged grievance of a man who forever imagines himself the victim, Trump relentlessly made things worse.

For three more days he persisted in demeaning a former beauty contestant. And in the early hours of Friday morning, he issued a series of manic tweets further disparaging Machado -- after suggesting that Clinton helped her become a citizen, he urged his followers to "check out" a sex tape featuring Machado which seems not to exist. So, once more, Trump had reduced the campaign to a reality show in which he played a slanderous bully with no grasp of his own poisonous psyche.

Obviously, Machado did not materialize from the ether. She was Clinton's weapon of choice, ready for deployment, and her past included unsettling, if unproven, accusations -- driving a getaway car for a boyfriend who had just attempted murder, then supposedly threatening a judge. But the proof of Trump's abusive conduct toward her was there for all to see, and his senseless attacks on yet another woman proved his inability to govern even himself.

Thus when Clinton remarked that "his latest Twitter meltdown is unhinged, even for him," she spoke for many more people than herself. After all, Clinton noted, "Really, who gets up at 3 o'clock in the morning to engage in a Twitter attack against a former Miss Universe?"

No one but Donald Trump. By doing so, he demolished the scripted persona his latest brain trust had scripted for him, buttressing Clinton's assertion that he is "temperamentally unfit to be president of the United States." Even Republican professionals felt the kind of muted horror expressed by Ohio State Chairman Matt Borges, "Can this thing just end - please?" The sharp GOP strategist Ana Navarro was more emphatic: "Forget being president. This guy isn't fit to take care of a puppy."

One doubts that Trump can take in what he's doing to himself. Increasingly, he is enabled by a soulless palace guard led by Rudy Giuliani, who now resembles a vicious and demented elder, screeching and flailing as his keepers administer sedatives. "Republicans", Giuliani opined with his now-habitual sneer, "are a bunch of frightened rabbits." Giuliani's better idea is to use Bill Clinton's sexual history to tear down his wife.

Never mind that, based on their own scurvy behavior toward women, Giuliani and Trump should avoid the subject like, well, scurvy. Giuliani's advice appeals to Trump's worst instincts -- the only instincts he has. And so he has segued from Machado to a personal attack against Hillary Clinton almost as ill-advised: that she was her husband's enabler. To which he adds this stunning assertion: ""I don't even think she's loyal to Bill..."

And so, as America watched, his descent into madness accelerated. The public crack - up came Saturday night.

Its predictable predicate was the kind of humiliations to which Trump, predictably, responds by losing control. His poll numbers -- as ever his chief measure of success -- were flagging. The media was dwelling on his floundering debate, accentuated by his irrational actions in its wake. And a leaked page from his tax returns in 1996 strongly suggested that, due to staggering business losses, he has paid no income tax for the last 20 years.

The result was a frightening foretaste of what a Trump presidency might portend. At a nighttime rally in Pennsylvania he went completely off the rails, the very portrait of a man cracking under pressure. Best simply to report, without elaboration, the events described by Jenna Johnson in the Washington Post.

Ignoring the script his handlers had prepared for him, he veered from one tangent to the next. He implied that Hillary Clinton was adulterous. Evoking his prior mockery of a disabled reporter, he imitated her loss of equilibrium at the 9/11 memorial service. He suggested that Clinton is "crazy." He opined that she should be in prison.

He wondered if he should have done another season of "The Apprentice" instead of running for president. He blamed his debate performance on a defective microphone, intimating that it was sabotaged. He invited the crowd to jeer the moderator, Lester Holt. He attacked "the dopes at CNN."

He again raised the specter of election fraud which would cheat him of the presidency. He invited his mostly white crowd to visit polling places in "certain areas" on election day, suggesting that they "watch" to see who was voting. "I hear too many bad stories," he informed them, "and we can't lose the election because of you know what I'm talking about."

Finally, this. After warning that Clinton was giving away the jobs of hard-working Pennsylvanians to please her wealthy donors, he said, "You're unsuspecting. Right now, you say to your wife: 'Let's go to a movie after Trump.' But you won't do that because you'll be so high and so excited that no movie is going to satisfy you. Okay? No movie. You know why? Honestly? Because they don't make movies like they used to - is that right?"

This is not a joke -- it actually happened. One quails at the thought of Chief Of Staff Rudy Giuliani saying, "Right, Mr. President."

No doubt one engine of this meltdown was the mortifying revelation about his taxes, fusing his seamy self-aggrandizement with his incompetence in business. To say the least, this ran counter to Trump's narrative. Tax avoidance, he asserted at the debate, "makes me smart." And after the New York Times revealed just how "smart" he had been, the craven Giuliani suggested that Trump had been unduly modest: "He's a genius - absolute genius."

Not so much. In the early 1990s, it turns out, Trump reported business losses so massive that they could shelter him from income taxes on nearly $1 billion. As a former head of the Congressional Budget Office remarked, "It's either a unique combination of bad luck or he's a terrible businessman or both. I don't understand how you can lose $1 billion and stay in business."

Here's how. Trump used the tax and bankruptcy laws to turn an epic series of business disasters into a tool of personal survival -- perhaps at the edge of legality -- while his contractors went unpaid and his investors lost their money. His avoidance of taxation is not evidence of acumen, but an undeserved reward for selfishness and ineptitude.

With this, a core truth about Donald Trump was confirmed at last. He is not a master builder who would make America great again -- he is a child of our corrupt tax code, stacked to insulate wealthy real estate developers from the consequences of failure. Genius did not save him -- loopholes and bankruptcies did, and at a cost to everyone but Trump. Little wonder that his tax proposals for America are designed to treat developers like Trump even better. In the words of another venal developer, Leona Helmsley, "Only the little people pay taxes."

They also vote.

Including the little people of Florida who happen to be Cuban. In mid-September, Trump courted anti-Castro Cubans by attacking President Obama's "one-sided deal" to normalize relations with Cuba. Last Thursday, a mere two weeks later, a well-documented report in Newsweek asserted that, in 1998, a Trump business enterprise had spent money in Cuba exploring business opportunities -- a violation of the legal embargo lifted by Obama.

The Trump campaign's evasive response was merely one more piece in a week-long mosaic depicting Trump's inner landscape. The last piece fell into place just yesterday -- an action by New York's Attorney General against the Trump Foundation.

The foundation has already been exposed for the sham it is -- a source of illegal campaign donations whose charitable impact is minimal and which, for the past eight years, has not been funded by Trump himself. Now, it transpires, the foundation is violating state law by soliciting donations without proper registration, enabling it to avoid the rigorous audits otherwise required by New York law. Wherever Trump goes, pathology follows

But some venues are far more dangerous than others. That is the larger point dramatized by the events of last week -- Trump's deeply disturbed behaviors most of all. The man who would be our president is a liar and a charlatan, devoid of conscience or empathy for others, alive to nothing but his own ungovernable desires, and beset by multiple pathologies which metastasize under pressure. The chapters of history are filled with such men, and they do not end well.

And so conservative newspapers have started shouting across the divide which separates Trump's supporters from reason. The Cincinnati Enquirer has supported Republicans for nearly a century; The Dallas Morning News since before World War II; The Houston Chronicle traditionally leans Republican. Citing Trump's temperament, all have endorsed Hillary Clinton.

In its 34 years, USA Today never endorsed the presidential candidate. After the events of last week, its editorial board wrote that Trump is "unfit for the presidency." They offered a bold-faced litany of disqualifications:

"He is erratic. He is ill-equipped to be commander-in-chief. He traffics in prejudice. His business career is checkered. He isn't leveling with the American people. He speaks recklessly. He has coarsened the national dialogue. He's a serial liar."

Seems like enough. But the morning after Trump's debate debacle, when The Arizona Republic endorsed a Democrat for the first time in its 126 year history, its editorial director cut to the quick of why: "There is something extraordinary about this Republican candidate that was making us all break from our history."

Whatever their reservations about Clinton, he explained, she "treats the office with respect. And Trump has no respect for the office that he seeks. If the leaders of our country don't respect our important institutions, no one is going to respect them. That's why he scares us."

Trump's conduct last week, frightening in itself, indelibly captured this difference. Hillary Clinton is not only competent, but eminently sane. Trump is neither.

He is not merely unqualified, though that is more than enough. Nor is he merely a dreadful human being. He is a very sick one, fighting to become the most dangerous man on earth.