Pope Francis waves to the faithful as he arrives in St. Peter's square for his weekly audience on June 3, 2015 in Vatican City, Vatican.National Journal

John F. Kennedy almost certainly would be both stunned and appalled to see the domestic political reaction to the encyclical on climate change issued Thursday by Pope Francis. He would find it hard to believe that the Catholics who are running for president were pressed even before the document came out to say if the pope's view would change their long-held stands on global warming. And he would be horrified at a rush by both conservatives and liberals to brand their political opponents as "bad Catholics."

As the nation's only Catholic president, Kennedy worked hard to make such questions unthinkable in an environment where Catholic officeholders in Washington were rare. But today, at a time of unprecedented Catholic success in national politics, they have become almost routine.

At least seven of the potential Republican candidates are Catholics—Jeb Bush, Rick Santorum, Marco Rubio, Chris Christie, John Kasich, Bobby Jindal, and George Pataki. All are aware that Republican primary voters are highly skeptical that climate change is man-made and are wary of proposed solutions that rein in fossil fuels. So when the leader of their church proclaimed the science of climate change settled and proposed radical changes to save the planet, the candidates were thrown on the defensive.

Bush, the former Florida governor, warned Iowans against mixing politics and religion. "I go to church to have my faith nourished, to have my faith challenged. That's why I go to Mass. I don't go to Mass for economic policy or for things in politics," he said bluntly.

Santorum, the former Pennsylvania senator who often pounces on any sign of anti-Catholic bias, was quick to dredge up Vatican mistakes from past centuries, hinting at past treatment of Galileo. "The church has gotten it wrong a few times on science," he said. "And I think we probably are better off leaving science to the scientists and focusing on what we're good at, which is theology and morality."

For some liberals, there was a clear opening to pay back Republicans by tweaking them on this break with the leader of their church. Many still chafe over GOP encouragement for the archconservative bishop of St. Louis who wanted to deny communion to Sen. John Kerry in 2004 when he was the first Catholic nominee for president since Kennedy.

This is not the way that Kennedy wanted Catholics in politics to operate. The political world was quite different in 1960. Then, there were only nine other Catholics in the Senate; today, there are 26, with 138 in the House. Then, there was a token Catholic on the Supreme Court; today, six of the nine justices are Catholic, and the Court includes not a single Protestant. Then, only one Catholic had ever won a major party nomination for president or vice president; today, the vice president is Catholic after an election in which both vice presidential nominees were Catholic.

None of that could have been foreseen when Kennedy gave perhaps the most important campaign speech of the post-World War II era. That was his address to the Houston Ministerial on Sept. 12, 1960.

"I believe," said Kennedy, "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, and no Protestant minister would tell his parishioners for whom to vote; where no church or church school is granted any public funds or political preference; and where no man is denied public office merely because his religion differs from the president who might appoint him, or the people who might elect him."

He added, "I believe in an America ... where no public official either requests of accepts instructions on public policy from the Pope ..." And, later, he said, "I am not the Catholic candidate for president. I am the Democratic Party's candidate for president who happens also to be a Catholic. I do not speak for my church on public matters and the church does not speak for me."

Today, it would be tough for any Republican to give such a speech in Iowa, where evangelical groups—often allied with conservative Catholics—demand a level of public religiosity that Kennedy would never recognize. That is what made Bush's comments in Iowa intriguing. For they could have been said by Kennedy.

"Jeb was out of the Kennedy handbook," said respected conservative strategist and Catholic Greg Mueller. "He's basically saying the same thing JFK said in 1960."

Mueller dismissed the notion that Republicans are uncomfortable disagreeing with the pope or are guilty of apostasy similar to Democrats who break with the church's teaching on abortion. "That's apples and oranges," he said. "If you're a Democrat and you are pro-abortion, you are clearly in violation of the dogma and teachings of the Catholic Church."

He predicted the debate over climate change spurred by Pope Francis' encyclical will pass quickly. "We're going to have a couple of days of coverage of this. I just don't think climate change is on the minds of the American people," he said.

John C. Green, director of the Bliss Institute of Applied Politics at the University of Akron and an expert on religion's role in politics, also thinks Bush's response to the encyclical was shrewd. "His argument is very much in the vein of the Kennedy speech," he said. But he noted that other Republicans have been harsher in their response and he sees no end in sight in the political war between liberal and conservative Catholics.

"Catholics on both sides have really been beating themselves up for about 20 years now," he said. "When the Democratic Catholics are pressing the Republican Catholics on climate change, in one sense that is just turnabout is fair play. Except that every turn of the issue agenda leads to increased polarization."

In one sense, the stakes are too high for the fight to subside. Catholics are the ultimate swing voters in presidential elections. They have gone with the winner in every election since 1972 with the exception of 2000, when they supported Democrat Al Gore.

There may be only one thing that restrains the battle and that was learned in the 2004 scuffle over whether Kerry should be denied communion. Most Catholics recoiled at that tactic. That October, I conducted extensive interviews with 30 Catholic voters in Cleveland in three focus groups. They were evenly split between Bush and Kerry supporters, conservatives and liberals, young and old. Just about the only thing that united them was opposition to the bishops trying to tell them how to vote.

"It's none of their business," said Kathleen Minadeo, then 41, a personnel clerk. "They can say what they want to say, but they can't tell me who to vote for." Harry Hewitt, then 53, who was a conservative Bush supporter in corporate real estate, said he "unequivocally" agreed with the bishops on abortion. But when it comes to the election, he said flatly, "The bishops should butt out."

A decade later, Republicans no doubt hope voters have a similar view about the latest encyclical from the bishop of Rome.

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