“Even if you flippin’ fries at McDonald’s,” Oprah Winfrey once said, “if you are excellent, everybody wants to be in your line.”

I thought of this quote when Donald Trump turned up yesterday at a McDonald’s restaurant in suburban Philadelphia to work a shift making French fries, then handing bags of food to drive-through customers.

As political stunts go, this might have been the best I’ve ever seen, because it served two very powerful purposes in the presidential race.

First, it reminded voters that his rival, Kamala Harris, has repeatedly boasted about having a summer job at McDonald’s to make her sound more relatable to her fellow Americans, but to date, not a single person has been able to verify this.

This is quite extraordinary given how specific she has been, with her campaign team stating that she worked at McDonald’s on Central Avenue in Alameda, Calif., in 1983 after her freshman year at Howard University, working on the cash register, french fries station and ice cream machine.

But then, she didn’t mention it in her memoir, nor does it appear on the 1987 résumé she submitted when applying for a position at the Alameda County District Attorney’s Office despite listing her other work experiences.

It was like it never happened at all!

Even more intriguingly, the New York Times reported on Sunday: “In subsequent years, Ms. Harris talked so little about her long-ago job at McDonald’s that even some of her friends and close aides did not know she had worked there.”

Hmmm.

Forgive me, but I smell the same gigantic, disingenuous rat that Trump’s been smelling about Kamala’s supposed McDonald’s career move.

And it matters because it goes right to the heart of the Democratic candidate’s persistent pitch that she is the truth antidote to fork-tongued Trump.

If you’re going to position yourself as a bastion of honesty, you can’t tell brazen, self-promoting “I’m middle class just like you” fibs about working at McDonald’s.

The second reason why Trump’s stunt worked so effectively is because McDonald’s is about the purest personification imaginable of the American free market dream — a place where everyone can afford to eat, and equally, where everyone has a shot at potentially running a McDonald’s franchise one day.

There are 13,562 McDonald’s restaurants in America, a third of all the McDonald’s outlets in the entire world.

They’re in all 50 states, spread across over 5,000 cities.

And they serve 25 million people a day, approximately 7.5% of the US population.

Staggeringly, nearly 9 out of 10 American households visited McDonald’s at least once in the past year.

And the No. 1 biggest-selling item on the menu is the original, basic french fries.

So when Donald Trump announced, “I’ve always wanted to work at McDonald’s” as he arrived yesterday, and then donned his apron to start preparing those very fries, he was tapping directly into a job that so many of his countrymen can instantly relate to.

Amazon’s billionaire founder Jeff Bezos worked at McDonald’s, as did the likes of Jay Leno, Pink, James Franco, Pharrell Williams and Olympic great Carl Lewis.

And so have millions of ordinary non-celebrity Americans.

McDonald’s is the great unifier, crossing all race, gender, age and creed divides.

And Trump was very clearly “lovin’ it” every minute he was a temporary employee of the iconic burger chain.

“I could do this all day,” he exclaimed. “I love McDonald’s, I love jobs, I love to see good jobs.”

Members of the carefully screened public who drove through to be handed free bags of food by the former, and possibly next, president were all lovin’ it too, looking thrilled by their interactions with their unlikely server.

One woman even thanked him for “taking a bullet for us.”

“To be successful,” Ray Kroc, who bought the company from the original founding McDonald brothers and transformed it into a global powerhouse, said of his business strategy, “you must be daring … and different.”

Well, Trump definitely pursued a daring and different campaign path with this stunt, and I think it paid off spectacularly.

For a privileged billionaire who’s never been seen cooking a meal in his life to put a shift in at McDonald’s like that was not just hilariously funny, it was also a powerful connective link to regular voters.

And to those who have mocked him for it or lambasted him for alleging Harris invented her own Golden Arches experience, I’m reminded of Kroc’s other business ethos: “If any of my competitors were drowning,” he said, “I’d stick a hose in their mouth and turn on the water. It is ridiculous to call this an industry. This is not. This is rat eat rat, dog eat dog. I’ll kill ’em, and I’m going to kill ’em before they kill me. You’re talking about the American way — of survival of the fittest.”

If Donald Trump wins the election in 15 days, as I believe he will, it may well be this stunt that won it for him.

And if he doesn’t, he sounds like the perfect guy to run a McDonald’s in the spirit of Ray Kroc!