What is truly frightening and largely unappreciated outside America is how much Trump's rabble-rousing resonates with ordinary Americans, especially Republican voters, and how it may not be so entirely out of line with the practice on the ground.
If you don't believe me ask Mohammad Tariq Mahmood, a British gym-owner who paid for his family, including nine children, to travel to Disneyland. Mohammad and his family were authorised to fly only to be stopped last week at the last minute in Gatwick by US officials and told to go home and unpack their bags. No explanation was given for the refusal, leaving most to assume that were the family not Muslim they would even now be waiting in a three-hour queue to have their picture taken with a man in a mouse suit.
If you're still unconvinced, have a look at the polls, the latest of which found that four out of five Trump supporters are in favour of the ban with most also believing American mosques should be shut down. Perhaps more worrisome is the fact that about one in three ordinary Americans, of all political persuasions, think Trump's Muslim ban is a good idea.
Trump calls himself a "builder". True, he parlayed his father's successful real estate development business into something even more successful. But his real business is not building, it's branding. As any marketing undergrad will tell you, the success of any brand depends on its "relevant differentiation" from all other brands on the market. Trump took a lesson from successful high-end retail brands - Nike, Gucci, and so on - and audaciously slapped his monosyllable on buildings that were costlier, bigger, and shinier than all the rest. His brand was never about "good taste". It was always about "winning".
Now he's applied his brand to a presidential candidacy.
Stay in a Trump hotel, buy a Trump condo, or vote Trump for president, and you are a winner. It says so right on the brand label.
Conversely, place your vote elsewhere, and you are a loser.
As Trump explains it, being a loser these days means you lose your job to an illegal Mexican immigrant or you lose your wife or daughter to an illegal Mexican immigrant rapist.
After the shootings in San Bernardino, California, on December 2, you became one of a nation of losers if you let any more Muslims come into the country. Fortunately, Trump had a brand-name fix for sale. Shut those Muslims down. Get them before they get to Disneyland.
Some will insist that what really sets Trump apart from other candidates is money. But not me.
Thanks to America's Super PAC (Political Action Committee) system, individuals, corporations, unions, and other organisations can legally make unlimited independent political contributions as long as they don't directly (wink-wink) fund candidates. So the cash is potentially there for any of the GOP anointed, whether it comes out of the candidate's own pockets or those of an incredibly wealthy donor class.
Having your own money does help, of course. Yet, so far, it almost hasn't mattered in the case of Trump. His well-established brand and outlandish pronouncements have garnered him so much free airtime that he's hardly had to dip into his billions.
Some fear that he could simply buy the White House with a personal cheque. He wouldn't be the first. George Washington, the very first president, was in today's valuations worth well over $1bn. And no one has ever raised questions about his buying the office. Now, Joseph P. Kennedy, Sr., did come pretty close to purchasing the presidency for his son. As Ronald Kessler pointed out in The Sins of the Father: Joseph P. Kennedy and the Dynasty He Founded (St Martin's Press, p. 376), JFK even joked about it: "I have just received the following telegram from my generous father: 'Dear Jack: Don't buy a single vote more than is necessary. I'll help you win this election, but I'll be damned if I'm going to pay for a landslide!'"
No, if anything, Trump's ability to self-finance may be the most positive feature of his candidacy. It implies that, if elected, he would come into office beholden to no special interests. As a candidate, he certainly bows to no one in the American "establishment." Twixt the Trump brain and the Trump mouth there is no pernickety censor, no pesky filter.
Some politicians lie. In America, a special form of political lying is deemed "political correctness," which is essentially saying the "right things" and avoiding the "wrong things" regardless of what you believe to be true.
Trump proudly claims to be politically incorrect. What his critics call bullying, racism, xenophobia, and unconstitutional demagoguery, Trump translates as "political incorrectness" - in other words, the truth that no one else dares to speak.
Branding garbage perfume does not make it smell any better but the scary thing is that we all have to take Trump's candidacy seriously because a great many Americans have told pollsters that they agree with everything Trump tells them, no matter how it smells.
Yes, just when you think Trump has finally crossed one line too many, he crosses another. On December 17, he cooed over what he took as an endorsement from everybody's favourite Russian dictator, Vladimir Putin. "If Putin respects me, and if Putin wants to call me brilliant, I'll accept that, and I'll accept it on behalf of our country."
When an uncharacteristically dumbfounded Joe Scarborough, co-host of MSNBC's Morning Joe, questioned Trump about why he would want the endorsement of someone who "kills journalists and invades countries," Trump replied: "Joe, there is a lot of killing going on; a lot of stupidity; and that's the way it is."
Later, he gave ABC's George Stephanopoulos a more thoughtful response, a reply, in fact, fit for a Mafia lawyer: "Nobody has proven that he's killed anyone. He's always denied it. It's never been proven that he's killed anybody."
In Putin, Trump does not see a head of state, a dictator, an invader, or a killer. He sees a kindred brand. And because the Putin brand is marketed in another country, it doesn't compete with the Trump brand, so the two can express limitless admiration for each other.
It's nothing personal. Just good business. After all, the value proposition both men offer is the same. Putin's promise is to Make Russia Great Again. At his rallies and on his website, Trump sells baseball caps that say - just above the visor - Make America Great Again. Outwardly, both brands thrive on winning. Inwardly, however, the driver of both is fear.
To win the American presidency, Trump needs to Make America Scared Again. So far, he's winning.
Peter Casey is founder and executive chairman of Claddagh Resources, an Irish-based global recruitment and search business. He is a panelist on RTE's Dragons' Den and has written a book on the Tata Group - one of the world's most successful multinational companies, which was published by Penguin Random House. Twitter: @CaseyPeterJ