The meeting between Pope Francis and President Obama at the White House continues a tradition going back nearly a century between U.S. presidents and the head of the Roman Catholic Church.
The talks are private, often personal and, always, they take place against the backdrop of the politics of the time. That was the case at the very first such meeting, at the Vatican, as Europe was recovering from World War I.
Woodrow Wilson, the growing Catholic Democrats in the U.S. and the first awkward moment between a president and pope
In January of 1919, President Woodrow Wilson was on a tour of Europe that lasted more than six months. The main purpose of the trip was the Paris Peace Conference, but Wilson's itinerary included Italy, as well.
Initially, there was no plan to visit Pope Benedict XV, a pontiff who was deeply involved in ways the church could help Europe rebuild and emerge from the darkness and destruction of the war years. But at the suggestion of an American cardinal, Wilson did go to the Vatican for an audience with Benedict.
They discussed the recovery effort, but politics were in the back of Wilson's mind as well, according to the Rev. Matt Malone, editor of America, a magazine put out by the Jesuit order of the Catholic Church. Malone notes the growing working-class Catholic population in U.S. cities at the time.
"You're beginning to see Catholics, who were basically European immigrants, as a force within the Democrat Party," Malone says, "and it was absolutely a part of the political calculation."
Wilson's Vatican stop also included the first awkward moment between a president and a pope. At the end of the meeting, an aide told Benedict it was time for him to bless the group, but Wilson, a Presbyterian, was not interested in being blessed. He turned to his staff and asked if there were any Catholics present. There were.
The Catholics knelt as the pope blessed those present. Wilson remained standing.
Eisenhower, the 40-year gap and JFK — still the only Catholic president
It would be 40 years before another president would visit the Vatican. That would be Dwight D. Eisenhower, who met with John XXIII. There were reasons for the gap — the Great Depression and World War II, for example. But there was also a persistent anti-Catholic bias in the U.S.
That's something candidate John F. Kennedy had to address in his 1960 campaign. He was asked about it by reporters and delivered a speech to put to rest worries that he'd be a tool of the pope.
"I believe in an America where the separation of church and state is absolute," Kennedy said, "where no Catholic prelate would tell the president, should he be Catholic, how to act."
Kennedy was — and remains — the only president who was Catholic. He, too, traveled to Rome and Vatican City as president, his motorcade driving past huge throngs of onlookers who crowded the sidewalks.
It was July 1963, barely four months before JFK's assassination, and for many American Catholics, it was a proud moment of reaffirmation of their faith and pride in their country. It was a relatively new pontiff Kennedy met that day, as Pope Paul VI had been coronated just two weeks earlier following the death of his predecessor.
LBJ, Carter and the first popes to visit the U.S. — and the White House
Two years later, Paul VI would become the first pope to visit the U.S., traveling to New York City, where he met with President Lyndon B. Johnson.
Since then every U.S. president has met with the pope, but it wasn't until 1979 that a pontiff visited the White House. Jimmy Carter was in office and welcomed John Paul II, calling him "our new friend."
"The people of our country have waited a long time for this meeting," Carter said.
Malone said this was perhaps the most important of all of the meetings between presidents and popes. Both were men of deep Christian faith. John Paul and Carter hit it off. The session also helped make possible the opening of diplomatic relations between the U.S. and the Vatican five years later.
John Paul II, "committed anti-communist and Cold Warrior," meets Reagan
Most important, in even that first meeting with Carter, is what was on the pope's mind, according to Malone.
"John Paul II was a committed anti-communist and Cold Warrior," Malone said. "He already had in mind that he wanted to enlist himself in the struggle to free the world of communism."
By 1981, the U.S. had a new president, Ronald Reagan. He was eager to join the young, charismatic pope in that effort. On a papal visit to the U.S. in 1987, Reagan was there to greet the pontiff as his plane landed in Miami, extolling John Paul's life and work.
"In Poland, you experienced Nazism and communism," Reagan said. "As pope, you suffered a terrorist attack that nearly claimed your life. Still, you proclaim that the central message of our time is not hatred but love."
The anti-war message for George W. Bush
In 27 years, John Paul held more than a dozen meetings with U.S. presidents. One of the most famous — and most uncomfortable for an American leader — came late in his life, in 2004 with George W. Bush.
The setting was the Vatican, and the pope was opposed to the U.S. war in Iraq. In an ornate ceremonial hall, John Paul and President Bush sat side by side, the pope clearly infirmed because of advanced Parkinson's disease, his hands shaking, his voice halting and barely intelligible, as he read a statement in English
It was hard to make out exactly what the pope was saying because of his ailment, but the message was clear — a strong condemnation of the war.
"It is the evident desire of everyone that this situation now be normalized as quickly as possible with the active participation of the international community and, in particular, the United Nations organization, in order to ensure a speedy return of Iraq's sovereignty, in conditions of security for all its people," John Paul said.
He also seemed to refer to then-recent revelations of the abuse of prisoners by U.S. personnel at the Abu Ghraib prison.
"In the past few weeks," the pope said, "other deplorable events have come to light, which have troubled the civic and religious conscience of all."
Despite the criticism, Bush later spoke warmly about the pope.
"For those of you who have ever met him," Bush said, "you know, I'm telling you the truth when I tell you, being in his presence is an awesome experience."
No president finds a pope who agrees with him on everything. That's true of Obama and Francis, too. But the relationship between popes and presidents is seen as important by both sides.
And politics always has a seat at the table.
Correction: September 23, 2015 12:00 am — An earlier Web version of this story incorrectly identified the pope with whom former President Dwight D. Eisenhower met as John Paul XXIII. It was John XXIII.