With all the books about President Trump, one mystery has been ignored. How did this supposed clown manage not only to learn Ronald Reagan’s economic formula but also carry it to the next level?

Bob Woodward has sketched a White House ruled by fear. Omarosa Manigault Newman has written a yarn about a president “unhinged.” Michael Wolff has penned a picture of “fire and fury.”

Yet none has even tried to address the elephant in the room — how Mr. Trump built the platform of economic growth and jobs that managed to crack the Democrats’ presidential-election “Blue Wall” and leave our newscasters agape.

That’s the scoop that Stephen Moore and Arthur Laffer are about to publish in their new book “Trumponomics.” It’s an inside account of what they call the “America First plan to revive our economy.”

It’s not due to hit the bookstores until October 30. You can bet, though, that the networks and the big Democratic papers are going to cover it with derision.

In other words, they’ll yet again ignore all voters who knew first hand that the policies of the Obama years had stranded Americans with high taxes and without jobs and too demoralized to look for work.

Both authors have been at this for a long time. Steve Moore is one of the foremost explainers of pro-growth economics, a veteran of multiple think tanks, the activist Club for Growth, and of the Wall Street Journal editorial board.

Economist Art Laffer drew the famed “Laffer curve.” That’s the diagram Reagan used to show that if top tax rates got too high, lowering them could ignite enough growth to spur more revenues.

The foreword to the book is by Lawrence Kudlow, who’d spent the early years of the Reagan revolution planning tax cuts from a cramped office in the White House.

Mr. Kudlow was originally to be a co-author. He dropped out after Trump named him to head the National Economic Council. That makes him what Messrs. Moore and Laffer call “arguably” the “most important economist in the world.”

Back in the summer of 2015, these three musketeers of economic growth founded, with Steve Forbes, a committee to, as they put it, “unleash prosperity.”

It wasn’t a Trump project. Their aim was to educate all candidates in tax cuts, spending limits, decreased regulations, sound money, the rule of law — and free trade.

Mr. Trump was flirting with protectionism. Yet in March 2016, when he was still a longshot, they got an invitation to meet the candidate in his office at Trump Tower.

What a surprise. The guy notorious for his bluster and insults turned out to be not only warm and earnest but brimming with questions — and prepared to hunch at his desk and listen.

The trio hit him hard on trade. They had been plumping for more legal immigration. Trump did listen, but on trade he put out his arms and argued back against China’s market manipulation.

Most important: They discovered that they were — my words here — in love with the same voters. That is, Americans of all backgrounds who were either working or hungering for the chance to work.

Mr. Trump asked the trio to take a look at his tax plan — and the rest is history. He eclipsed the field to get the GOP nomination, then pierced the blue wall, won his tax cuts, and ignited his boom in jobs and growth (and wages), all with a stable dollar.

This story is not only about Messrs. Moore, Laffer, and Kudlow educating Mr. Trump. It’s also about Mr. Trump doing the educating (and surprising). Out on the campaign trail with the candidate, the musketeers were startled when he kept thousands waiting while he met with a paralyzed child who could communicate only by blinking.

Messrs. Moore and Laffer credit Steve Bannon with warning that the GOP had lost touch with its own voters. Yet Democratic economists — Larry Summers, say, or Paul Krugman — lacked for a clue as to how to exploit that.

The authors reserve judgment as to how it will all work out. The timing of their book suggests they grasp that the vote next month could have a lot to do with that.

They paint President Trump as no ideological conservative, far more of a businessman than an economist. They share with Mr. Trump, though, what Reagan shared with the American people — an incorrigible optimism.

This column first appeared in the New York Post.