Critics of the United States have argued for decades that our foreign policy, beneath its showy cloak of spreading freedom, is, and always has been, naked imperialism. In “A People’s History of the United States” — among the most influential books of the past 40 years — Howard Zinn popularized this analysis for two generations of high school and college students, and for many of their teachers.

For example, of the pillars of the post-World War II Western alliance — the Truman Doctrine, the Marshall Plan and so on — Zinn wrote: “The victors [of World War II] were the Soviet Union and the United States. . . . Both these countries now went to work — without swastikas, goose-stepping, or officially declared racism, but under the cover of ‘socialism’ on one side, and ‘democracy’ on the other, to carve out their own empires of influence.”

In Donald Trump, we have the first president to embrace this disillusioned take on the United States’ role in the world, in which democracy gets bracketed by knowing quote marks while empire is baldly stated. There is no higher purpose in Trump’s approach to foreign policy: it’s all about the Benjamins. In the Middle East, we ought to “take the oil,” while in Europe and the Pacific we should be paid for the peacekeeping troops we’ve deployed. Foggy Bottom and the Pentagon should be profit centers.

Trump’s original foreign policy team mistakenly believed this attitude was a result of gaps in his education. My Post colleagues Carol Leonnig and Philip Rucker, in their new book, “A Very Stable Genius: Donald J. Trump’s Testing of America,” detail a tumultuous meeting six months into Trump’s term in which Rex Tillerson and Jim Mattis — secretary of state and defense secretary, respectively, at the time — led a remedial tutorial session. “Trump appeared peeved by the schoolhouse vibe,” Leonnig and Rucker write mildly, and things quickly went off track.

The mention of troops and missile defenses in South Korea provoked this from the president: “We should charge them rent. We should make them pay for our soldiers. We should make money off of everything.”

The topic of NATO brought up the president’s belief that the United States should be paid for the security it provides. “We are owed money you haven’t been collecting!” Trump scolded the briefers. “You would totally go bankrupt if you had to run your own business.”

(A pause here to note that bankruptcy, unlike foreign policy, is a subject Trump knows from experience. Now, back to the briefing.)

Regarding troops in Iraq, Trump demanded: “We spent $7 trillion . . . Where is the f---ing oil?” Ultimately, the president grew so angry that he scathed the gathered brass, which included the chairman of the Joint Chiefs of Staff and other top national security officials, as “dopes and babies.”

Two and a half years later, the lead briefers are in private life. And Trump still runs the show.

Much is made of Trump’s aversion to his predecessor, Barack Obama, but this crudely mercenary approach to the world is more at odds with the doctrine of President George W. Bush. His second inaugural address in 2005 defined the United States’ global goals in purely idealistic terms. The purpose of foreign policy, Bush said, is “to help others find their own voice, attain their own freedom and make their own way.” And he went further, in words Trump surely would consider to be the height of dopiness:

“Our country has accepted obligations that are difficult to fulfill and would be dishonorable to abandon. Yet because we have acted in the great liberating tradition of this nation, tens of millions have achieved their freedom.”

Many years of stalemate and setbacks, blowback and body bags, form the bridge from Bush’s high-flown foreign policy to the money-grubbing cynicism of Trump. Lost between the two extremes is the fact that expanding liberty is not just good for the soul; it’s good for the wallet, too.

Look back at the quote from Zinn’s book. The author puts Soviet socialism and U.S. democracy inside quotation marks to signal that they were empty words masking the realities of empire. But they weren’t two doors leading to the same dystopia. The economies of the Soviet sphere, in which liberty and individualism were stifled, lagged far behind the economies of the U.S.-led West. Freedom paid a healthy dividend.

It’s clear by now that Bush bit off more than the United States was ready and able to chew with his ambitious, even reckless, Freedom Agenda. But Trump’s imperialism is an extreme overreaction — too extreme — and may prove more damaging over time. The president of the United States is now ratifying indictments leveled by some of the country’s harshest critics: that we are a nation of plunderers out for ourselves; that our talk of ideals is a smokescreen to hide our rapacity; that the world is wise to guard its wallet and check its receipts whenever Uncle Sam comes around.

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