NBC/ASSOCIATED PRESS Donald Trump and his aides face candidates for the job of "The Apprentice" in this undated publicity photo from the TV show.

WASHINGTON ― For the past year, Donald Trump has been selling himself to Republican voters and party leaders as a master developer, casino mogul, airline executive and all-around brilliant businessman.

What they didn’t hear much about, though, was his single greatest talent: master self-promoter.

Now, with the general election just three months away, they are learning they may have been sold a bill of goods. That Trump was actually a so-so developer. That his casinos failed and pushed him to the edge of personal bankruptcy. That his airline was a money-losing vanity project that he eventually lost when he missed loan payments. That his business acumen, far from brilliant, is now fodder for millions of dollars’ worth of negative TV ads.

“He is, as someone said, the hobo’s idea of a billionaire,” said Rick Wilson, a Florida political consultant who is now working for independent candidate Evan McMullin. “I’ve had donors say: ‘I’m a billionaire. Trump’s a clown with a credit card.’”

I’ve had donors say: ‘I’m a billionaire. Trump’s a clown with a credit card.’ Rick Wilson, Florida political consultant

“Trump is the master of creating a perception that he is successful, when he has used aggressive lawsuits and multiple bankruptcies in attempts to mask huge failures,” said Texas Republican consultant Matt Mackowiak.

For his part, Trump continues to insist he’s worth more than $10 billion, despite outside reviews that calculate his net worth at less than half that. A National Journal analysis of his finances found that he would have been far richer if, when he took control of his father’s empire in 1974, he had instead taken his share and merely put it into a stock market index fund.

Yet for millions of Republican voters, Trump’s self-proclaimed business savvy and great wealth ― as seen on television for years and validated by party leadership last autumn ― were major reasons for backing him over more than a dozen Republican governors and senators.

In New Hampshire last June, 67-year-old janitor Steven Sweeney said: “The Donald is going to shake things up. He’s got money. They can’t buy him. They’re not going to be able to push him around.”

In Des Moines, Iowa, last August, fairgoer after fairgoer dropping corn kernels into Trump’s jar as part of a straw poll said his business experience was what was needed in the White House.

Now, nomination in hand, Trump’s sway over his hardcore supporters may have only strengthened. One, a barbershop owner in St. Clairsville, Ohio, the site of a recent Trump campaign rally, seemed genuinely distraught at the suggestion that Trump was not as successful as he claimed.

“Mr. Trump is worth every dollar he says he is,” said the barber, giving only his first name, Kent. “Mr. Trump is a man of his word.”

Unfortunately for Trump and the Republican Party, the Kents of this country make up only a fraction of the voters Trump will need to win in November. As for the non-Kents ― particularly voters in the half dozen battleground states this year ― they will have been flooded with tens, even hundreds of millions of dollars of advertising using Trump’s business record against him.

I broke the unspoken code of confidentiality with Donald Trump on Art of the Deal because I truly believe his election imperils the planet. Tony Schwartz, ghostwriter, The Art of the Deal

Recent polling by The Huffington Post and YouGov shows that Democrats and independent voters, the groups that Trump must start persuading, are already receptive to that unflattering message.

While 70 percent of Republicans believe Trump is at least as rich as he says he is, only 44 percent of Democrats and independents believe that. Perhaps even more worrisome for Trump: While 65 percent of Republicans call him “very successful,” only 41 percent of independents and 27 percent of Democrats do so.

“He’s the master of the long con, pretending to be something he isn’t to scam the next victim,” Wilson said. This time, he added, the victim is the GOP itself.

Trump businesses tanked, but Trump’s brand soared

Although Trump may not really be a brilliant businessman, he played one on TV. For over a decade, his primetime series made his success part of the popular culture, bringing him into as many as 28 million living rooms a week. Starring in “The Apprentice” and its follow-up, “The Celebrity Apprentice,” Trump played an authoritative businessman making rational decisions. Never mind that the tasks the contestants had to perform ranged from the menial to the ridiculous. Trump himself, week after week, was the show’s voice of informed reason, making a tough but fair decision at the end of each episode.

The series itself was created by Mark Burnett, the producer of the “Survivor” reality TV show. He came up with the idea after reading Trump’s book, The Art of the Deal, which portrayed Trump as the shrewd, level-headed builder of a vast and profitable business empire.

That best seller was the first real vehicle pushing Trump’s celebrity beyond the reach of the New York City tabloids. It’s written in an easy, sometimes self-deprecating style ― which essentially makes it a work of fiction, according to Trump’s ghostwriter.

Tony Schwartz, who split millions of dollars with Trump from the book’s earnings, came forward last month, saying he had grown alarmed that Trump could actually win the presidency based on the character Schwartz had created.

“I broke the unspoken code of confidentiality with Donald Trump on Art of the Deal because I truly believe his election imperils the planet,” Schwartz wrote in a July 27 tweet.

In a New Yorker piece, Schwartz described a man unable to focus for any period of time and driven by a compulsive need for more money and more attention, to the point of reckless behavior.

If he were writing the book today, he said, it would be called The Sociopath.

Indeed, within a few years of the book’s 1987 release, Trump’s empire was on the verge of collapse. His casinos in Atlantic City were bleeding money. Trump had personally guaranteed nearly $1 billion in business loans, which were now threatening to put him into personal bankruptcy. Over a period of years, Trump’s empire shrank as lenders made him hand over ever-larger portions of his holdings and forced him to give up personal extravagances like his 281-foot-yacht. They even put him on an allowance.

With his credit shot, Trump’s business model shifted away from building things and consolidated instead around collecting a salary and profits from his television show, membership dues from his golf courses and fees for the use of his name on various hotels and condominiums that he did not own.

The Trump “brand,” thanks to his aggressive and constant promotion, had become his primary business line.

None of his defeats made him change the way he presented himself. In every speech, every debate, every interview, Trump brags about his success: his “phenomenal business,” his “tremendous cash flow,” his “very low debt.”

“I built a phenomenal business with incredible, iconic assets, one of the really, truly great real-estate businesses,” Trump said at last autumn’s Reagan Library debate.

Republican voters believed him.

“He’s a great builder,” said retired contractor Frank Savino at Trump’s very first “house party” in New Hampshire last summer. “He means what he says, and he says what he means.”

GOP leaders bought the myth, now stuck with it

That the average American tended to believe Trump’s boasts heading into last summer is perhaps understandable. After all, that was the proposition underlying his reality TV show for 12 years.

But what put Republicans into the box that traps them today is the failure of party leaders and Trump’s primary rivals to challenge that premise back when there was still time. During the crucial early debates last year, most of the other candidates ― assuming that Trump’s popularity would fade as the actual voting drew closer ― avoided attacking Trump. Even more important, they acknowledged his business success as a given.

“I love Donald Trump. He is a good man,” former Arkansas Gov. Mike Huckabee said at the October debate in Boulder, Colorado. “I’m wearing a Trump tie tonight. Get over that one, OK?”

The party’s top officials, meanwhile, were so fearful of Trump’s purported net worth and a threatened third-party run that chairman Reince Priebus traveled to Trump Tower and secured Trump’s signature on a pledge that he would support the eventual nominee. (Trump repudiated the pledge this spring, citing the party’s unfair treatment of him.)

While other candidates eventually starting calling Trump a liar and a con man, top Republican officials, advisers and donors continue to this day to believe Trump’s self-portrait of a business genius.

“He builds buildings. He runs a large business,” Andy Puzder, the CEO of the company that owns the Hardee’s and Carl’s Jr. restaurant chains, told HuffPost recently. “He certainly has all the indications of wealth.”

Supply-side economist Stephen Moore, one of Trump’s economic advisers, pointed to Trump’s numerous buildings as proof of his success ― seemingly unaware that many had nothing to do with Trump beyond sporting his name on a sign. “One of the things that he is a master at is branding,” he said. “His business skills are unrivaled.”

A great irony for Republicans is that four years ago they nominated a candidate who actually did have great business skills. For those who believe that running a successful presidential campaign requires a no-nonsense mindset to make informed decisions, Mitt Romney possessed that in spades ― and still lost the popular vote by a significant margin, thanks to demographics that are tilting ever more drastically against Republicans.

Four years later, with fewer than 90 days left before the election, the party is stuck with Romney’s opposite: an at-best mediocre businessman, with an all-nonsense, all-the-time approach to campaigning based primarily on his whims at any given moment.

Republican leaders concede privately that it is next to impossible to make Trump accept advice and that even to try risks putting him in a foul mood that makes the effort counterproductive.

To ghostwriter Schwartz, who followed Trump around for 18 months gathering material for The Art of the Deal, none of this is surprising.

“Trump doesn’t take advice from anyone. Ever. That won’t change. He is who he is. He won’t reset because he can’t,” Schwartz tweeted on Aug. 3. “Never thought I’d say this: Trump is worse today ― harsher, more erratic, more grandiose ― than when I first met him. And he was bad then.”

Editor’s note: Donald Trump regularly incites political violence and is a serial liar, rampant xenophobe, racist, misogynist and birther who has repeatedly pledged to ban all Muslims ― 1.6 billion members of an entire religion ― from entering the U.S.