Pope Francis waves as he leaves at the end of his weekly general audience in St. Peter’s Square at the Vatican on June 17, 2015. (Andrew Medichini/AP)

For more than half a century, Catholic politicians in the United States have regularly been put in awkward positions on the question of how closely they would — or should — follow the dictates of the Vatican.

Until recently, Democrats usually were the ones to feel the most heat. But now it is the turn of Republicans, thanks to Pope Francis, the charismatic and activist pontiff who is set to visit the United States in September.

The pope’s 192-page call to action Thursday, which blames the burning of fossil fuels and human activity for climate change, is the latest example of how Francis has become part of the political debate in a season in which no fewer than five Catholics may seek the Republican presidential nomination.

“The Earth, our home, is beginning to look more and more like an immense pile of filth,” Francis wrote.

Previously, he also condemned inequality as “the root of social evil” and said the problems of the poor should be “radically resolved by rejecting the absolute autonomy of markets and financial speculation.”

Republican presidential candidate Jeb Bush said this week he doesn’t take cues from the pope on climate change: “I don’t go to Mass for economic policy or for things in politics.” (Steve Pope/Getty Images)

While social justice has long been a pillar of Catholic doctrine, that kind of rhetoric in the document sounds anti-capitalist to many on the right.

“Essentially, what this papal encyclical is saying is that every Catholic should vote for the Democrat Party,” conservative radio host Rush Limbaugh said Tuesday, using the name for such a document from the pope. “That’s what it is. How else do you interpret it when the pope comes out and sounds like Al Gore on global warming and climate change?”

Catholic politicians face a balancing act, given the popularity of a pope who had an approval rating of 86 percent among U.S. Catholics and 64 percent among Americans overall in a recent poll conducted by the Pew Research Center.

Former Florida governor Jeb Bush, a Catholic convert campaigning in Iowa, was asked Wednesday about the papal document.

“I respect the pope. I think he’s an incredible leader, but I think it’s better to solve this problem in the political realm,” Bush said. “I’m going to read what he says, of course. I’m a Catholic and try to follow the teachings of the church.”

Later, Bush added: “I don’t go to Mass for economic policy or for things in politics.”

GOP presidential candidate Rick Santorum says it is “sometimes very difficult to listen to the pope and some of the things he says.” (Louis Lanzano/Bloomberg News)

His comments carried an echo of the argument made by then-Sen. John F. Kennedy in 1960 as he addressed a skeptical audience of protestant ministers in Houston.

“I believe in an America where the separation of church and state is absolute; where no Catholic prelate would tell the president — should he be Catholic — how to act,” said Kennedy, who eight weeks later would become the first Roman Catholic elected to the White House.

For Republicans, the dilemma posed by Francis is compounded by the fact that many on their side have argued that religious faith should have a greater role in politics. In 2012, Republican presidential contender Rick Santorum made his own trip to Houston to argue that Kennedy had been wrong.

“On that day, Kennedy chose not just to dispel fear, he chose to expel faith,” Santorum said. “The idea of strict or absolute separation of church and state is not and never was the American model.”

But Santorum, who is running again in 2016, has said that some of what Francis says — for instance, that Catholics should not believe that their faith requires them to reproduce like rabbits — grates on him.

“It’s sometimes very difficult to listen to the pope and some of the things he says off the cuff, and this is one of them,” Santorum, a father of seven, told radio host Hugh Hewitt in January.

Other Catholic candidates and would-be candidates for the 2016 GOP nomination also have found themselves at odds with Francis.

Sen. Marco Rubio (R-Fla.) has chided the pope for helping broker President Obama’s deal to normalize U.S. relations with Cuba. And when the pope expressed support for the theory of evolution, Louisiana Gov. Bobby Jindal (R) declined to comment on whether that would affect his support for a bill allowing his state’s schools to teach creationism.

About 1 in 5 adult Americans identify themselves as Catholic, according to the Pew Research Center, and they have long been considered a key swing voting group.

But a 2012 Pew analysis suggested that relatively few of their votes — those of white Catholics who say they are moderate — are actually up for grabs.

Hispanics and other Catholic minorities generally vote Democratic; white Catholics who call themselves conservative vote for Republicans; white Catholics who say they are liberals are consistent supporters of Democrats.

Until recently, Catholic Democratic politicians have more often been the ones on the defensive against church leaders, particularly over abortion. In 2004, the archbishop of St. Louis warned Democratic presidential nominee John F. Kerry, an abortion-rights supporter, “not to present himself for Communion” — an ostracism that canon law reserves for “those who obstinately persist in manifest grave sin.”

Francis’s encyclical on climate change garnered praise this week from many Democrats, including President Obama, who issued a statement Thursday, and former Maryland governor Martin O’Malley, a presidential candidate who is Catholic.

House Democratic leader Nancy Pelosi (D-Calif.), another Catholic, said the pope’s message was written “with beauty, with clarity and with moral force.”

But Pelosi has often been a critic of the Vatican on abortion. “I love the pope. I have the highest regard for the pope,” Pelosi said in 2003 of John Paul II. “But I don’t think that a lot of guys should be calling the shots.”

The environment is not the only issue on which the church is becoming more visible in a way that pleases many Democrats. Many, for instance, expect that Francis’s visit to the United States will intensify the national conversation about income inequality.

On Monday, several prominent Catholic clerics — including Cardinal Donald Wuerl, the archbishop of Washington, who is said to be one of the pope’s closest U.S. confidants — appeared at a daylong conference at the AFL-CIO’s Washington headquarters aimed at forging a closer working relationship between the church and labor unions.

“For the labor movement, Pope Francis’s messages are exactly what we need,” AFL-CIO President Richard Trumka told a roomful of priests, progressive activists and reporters.

But conservatives say that is not a welcome development. Nor is it one that Francis intends as he prepares to visit amid an intensifying presidential campaign, they said.

“He’s not coming here as a campaign consultant, and it frankly demeans his office if people try to recruit him for partisan purposes,” said George Weigel, a Catholic theologian affiliated with the conservative Ethics and Public Policy Center.

But Weigel conceded that it is probably inevitable that the visit will take on a political cast. “When you have a political community like ours, where there is pretty much a 50-50 divide, people are going to look for whatever they can get their hands on to move things one or two ticks in their direction.”

Michelle Boorstein and Ed O’Keefe contributed to this report.