By Froma Harrop

A friend of mine, an expert car mechanic, once told me of losing $30,000 in a commodity deal. It was one of those investment swindles then making the rounds. I asked my friend whether he felt angry.

“No,” he answered. “I could have tripled my money.”

He had no idea that he had been hosed.

Every successful scam ends with a “blow-off.” That’s when the con artist, having relieved the mark of his money, gets rid of the victim. That can be done several ways. Often the chump is too embarrassed to complain. Or he can be intimidated into silence.

The ideal victim is the one who, like my friend, gets taken but doesn’t know it. Such trusting people often come back for more.

Donald Trump is now at the blow-off stage of his hustle to win the support of blue-collar whites.

He started with an in-your-face double cross, filling his administration with the very Wall Street financiers he promised to defang. Then he chose for labor secretary Andrew Puzder, a fast-food executive hostile to a decent minimum wage and several other worker protections.

Blue-collar America has indeed been hurt by mass immigration, especially the illegal kind. On this issue, Trump campaigned as a hard-liner. But Puzder has been a champion of cheap foreign labor. The department he would head is supposed to punish employers who hire undocumented workers.

Trump’s low regard for working stiffs hasn’t exactly been a closely held secret. He ran for president having already employed illegal labor, stiffed his contractors and defrauded the little guys attending Trump University. So how did he get their vote?

“There’s nothing a con artist likes better than exploiting the sense of unease we feel when it appears that the world as we know it is about to change,” Maria Konnikova writes in her book “The Confidence Game.” Globalization and automation have put factory workers under enormous stress.

Trump checked off all boxes in the art of the con. 1) Learn what the target wants. 2) Play on that desire. 3) Create an emotional foundation based on rapport and an illusion of empathy.

The revolution in information technology also helps. The Trump campaign spread fake news to trap low-information voters in an alternate reality it could control.

As the famous imposter Frank Abagnale — inspiration for the movie “Catch Me if You Can” — said, “What I did 50 years ago as a teenage boy is 4,000 times easier to do today because of technology.”

A common trait among fraud victims is a desire to believe that things will work their way. Vox asked Kentuckians dependent on Obamacare why they had voted for Trump despite his repeated vows to repeal the Affordable Care Act.

“We all need it,” a woman responded. “You can’t get rid of it.” Right.

One can see why Trump would find casino gaming a business to his liking. Modern electronic slot machines are programmed to trick their marks into believing they barely missed the jackpot. The pigeon thinks: “I almost won the big one. Better keep dropping money in this machine.”

How will labor respond to the Trumpian blow-off? Some may resist. The president of the local steelworkers union flatly announced that Trump “lied his a** off” about the number of jobs he saved at the Carrier plant in Indianapolis. Trump hit back with an insulting tweet, and others threatened the labor leader’s family.

Some may quietly obey rather than expose themselves to such intimidation. And still others will continue to believe that Trump has their interests at heart — or that he’s not doing what he’s doing.

One wishes a better outcome for American workers of all colors. They’ve suffered enough.

Email Froma Harrop at fharrop@gmail.com.