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From the beginning of a presidential campaign that opponents and pundits alike once derided as a joke, Donald Trump decided that his greatest strength was his total lack of a quality all his opponents had to a greater or lesser extent: shame.
Brazen shamelessness and a disrespect for the boundaries - often of decency and propriety - that are normally the defining characteristics of all mainstream politicians have propelled Mr Trump to the threshold of the Republican presidential nomination.
A refusal to respect sacred cows has enabled the all-conquering property mogul and television reality star to leave a succession of once-mighty high profile casualties in his wake.
They include: Senator John McCain, former Republican presidential candidate and war hero, ridiculed for being shot down by North Vietnam and becoming a prisoner of war; Megan Kelly, Fox News host, on the receiving end of relentless personal and misogynistic attacks after confronting the candidate about his attitude to women; Jeb Bush, scion of one of America’s most successful political dynasties and once thought the likely nominee, mocked as “low energy”; Mitt Romney, the failed 2012 Republican nominee, vilified after attacking Mr Trump’s credentials; Marco Rubio, the Florida senator, swatted away contemptuously as “little Marco”; and last but not least, Ted Cruz, the Right-wing Texas senator who became the party establishment’s last hope of stopping the Trump juggernaut only to be flattened by a fusillade of abuse that included attacks on his wife’s looks, fanciful smears of his father’s role in the assassination of JFK and himself denigrated as “lyin’ Ted”.
In none of this has Mr Trump behaved like a traditional politician - and the result has been an almost unbroken run of success that has confounded Republican party grandees who have despaired of stopping him.
As for the vaunted “brokered convention” where a compromise nominee could be parachuted in to avert the nightmare of a Trump candidacy, that notion - as Mr Trump himself would say - is now surely for losers. He is within easy touching distance of the 1,237 delegates he needs to make his nomination inevitable and will almost certainly reach that figure before July’s convention in Cleveland.
It all seems too fantastical to comprehend.
Yet hindsight shows that Mr Trump deployed his absence of shame to offer simplistic populist solutions on issues that have shaped a fearful and resentful public mood - and reaped electoral dividends.
Immigration
A key concern to conservative working-class voters, Mr Trump played to base instincts. Mexico was sending “drug dealers and rapists” to America, he said in language that drew widespread condemnation but clearly resonated. In response, he would build a “beautiful” wall on the border and force Mexico to pay for it. Some 11 million illegal immigrants would be rounded up and forcibly deported.
Terrorism
After November’s deadly jihadist assaults on Paris Mr Trump first repeated the discredited trope that “thousands” of American Muslims celebrated the 9/11 attacks - a shameless lie. When that brought the inevitable denunciations, he went further than any other candidate would ever have dared - by proposing a blanket ban on all Muslims entering the United States, a blatantly discriminatory policy that nonetheless played on the fears of a significant segment of Republican voters.
Trade
Mr Trump has depicted the loss of American jobs as a result of flawed trade deals with China, Mexico and others and vowed to stop what he has represented as the sell-out of the country by a clueless, weak leadership. Trade agreements would be torn up, he has said. This has chimed with a portion of the electorate left bewildered by the pace of change wrought by the digital economy - and unpersuaded by arguments that similarly disruptive processes are wreaking just as much havoc elsewhere.
Protesters
Mr Trump’s unconcealed incitement of violence at his rallies and calls for demonstrators to be “punched in the face” and “carried out in stretchers” may be ugly, but they carry a raw emotionalism that has greater popular appeal than cerebral argument and conveys an image of strength. History shows repeatedly that demagoguery has its uses - even in the electoral arena.
In all the above categories, Mr Trump’s approach has been extreme - and in policy terms, impractical. But they invariably dominated headlines, which enabled him to lay waste to his opponents.
The presumptive Republican nominee now promises to turn “presidential” and says America is a divided nation which needs to be brought together - an endeavour which his prior conduct appears ill-designed to achieve.
With a wider and much more sceptical electorate now about to face him than the one he was dealing with in the Republican primaries, his best path to success would appear to be changing it - and quickly. Position himself as a healer, rather than an agent of division; get the alienated Republican establishment on his side, however belatedly.
The signs that he can do so are unpromising. With Hillary Clinton now in his sights as the probably Democratic nominee, Mr Trump is already indicating that he will stick to his tried and trusted instincts of confrontation and abuse.
“I haven’t devoted any time, effort, energy to Hillary yet,” he told the Washington Post. When he does, it is unlikely to be in the service of dryly debating policy. “Her past is really the thing, rather than what she plans to do in the future,” Mr Trump added of an opponent he has already tagged “crooked Hillary” and “incompetent Hillary”.
Mrs Clinton’s past - and that of her husband - does indeed offer a rich seam. But signalling an intention to mine it is not the mark of a candidate about to be shamed into turning over a new leaf.