Pope Francis has stepped into a long-simmering American political feud over economics.

In the English-language version of a new message about re-orienting the Catholic Church's evangelical efforts released to worldwide notice last week, the pontiff criticized economic inequality and offered a harsh assessment of “trickle-down theories” of economics.

Those theories, Francis wrote, express a “crude and naïve trust” in the “prevailing economic system” while “the excluded are still waiting.”

In using the phrase “trickle-down,” a term loaded with historical meaning in U.S. economic discourse, Francis stepped on some conservatives' toes with his new apostolic exhortation, Evangelii Gaudium — The Joy of the Gospel, in English.

Writing on his personal blog on Saturday, Harvard economics professor and former George W. Bush adviser N. Gregory Mankiw took exception to the phrase, calling the pope's use of it “a pejorative used by those on the left to describe a viewpoint they oppose.”

“It is sad to see the pope using a pejorative, rather than encouraging an open-minded discussion of opposing perspectives,” he wrote. Mankiw, a top Republican-aligned economist, also noted the evidence that “free-market capitalism” has lifted people out of poverty, and in doing so has been “a great driver of a more moral society.”

On Monday, conservative talk show host Rush Limbaugh devoted multiple segments of his program to pushing back against the pope's statements, saying that "this is just pure Marxism coming out of the mouth of the pope" and commenting that "this is really befuddling because he's totally wrong — I mean, dramatically, embarrassingly, puzzlingly wrong."

English-speaking free-market economists consider the term “trickle-down” a tendentious label for their ideas, said Brian Domitrovic, a professor of history at Sam Houston State University in Texas who has written about the rise of supply-side economics.

“This is an epithet, just like ‘voodoo economics’ was in the ‘80s,” Domitrovic said. “It doesn’t belong in a papal document.”

Domitrovic, a Catholic who describes himself as well-disposed to Francis, suggested that there might have been “some kind of mischief” in the English version of the document’s use of the term “trickle-down,” echoing the concerns of other English-speaking readers that something may have been lost in translating the document from the original Spanish.

The term used in the Spanish version of the document was “derrame,” a word that translates to “spill.”

"Derrame" is “generally what's used for trickle-down-economics in Spanish” and doesn’t have an alternative economic connotation for Spanish-speakers, said Jake Johnston, a research associate on Latin American economic issues for the Center for Economic and Policy Research.

Variants of the term "trickle-down" have been used as populist disparagements of economic ideas for more than a century in U.S. politics, from William Jennings Bryan and Lyndon Johnson to President Obama. During last year's presidential campaign, Obama derided his Republican opponent Mitt Romney's economic agenda, saying that "for much of the last century, we have been having the same argument with folks who keep peddling some version of trickle-down economics."

Francis’ comments on economics have to a large extent overshadowed the bulk of message he intended to impart.

“I wish to encourage the Christian faithful to embark upon a new chapter of evangelization marked by this joy, while pointing out new paths for the Church’s journey in years to come,” Francis wrote in the opening paragraphs of the document.

But it is his evocative denunciations of various inequalities and social ills that have dominated the U.S. media's accounts of his writing.

“Today we also have to say 'thou shalt not' to an economy of exclusion and inequality. Such an economy kills,” Francis wrote. “How can it be that it is not a news item when an elderly homeless person dies of exposure, but it is news when the stock market loses two points?”

In a subsequent passage, Francis wrote, “As long as the problems of the poor are not radically resolved by rejecting the absolute autonomy of markets and financial speculation and by attacking the structural causes of inequality, no solution will be found for the world's problems or, for that matter, to any problems. Inequality is the root of social ills.”