They speak the same economic language, focused on inequality and the plight of the underprivileged. One's a spiritual leader; the other a political one. One's popularity is stratospheric. The other's, well, not so much.
When U.S. President Barack Obama meets Pope Francis on Thursday at the Vatican, the six-year president would not be blamed for seeking some reflected glory from a pope who, one year into his pontificate, is viewed as an agent of change in the Roman Catholic Church.
- Has 'rock star' Pope Francis really launched a revolution?
- How Pope Francis is reshaping the Vatican
- The Vatican radical: James Carroll on Pope Francis
Obama is the ninth president to make an official visit to the Vatican. His audience marks a change of pace for the president, who has devoted the past three days of a weeklong, four-country trip to securing European unity against Russia's aggressive posture toward Ukraine.
The pope whom Obama will sit with this time is a different pontiff than the last one to host him. Obama visited Pope Benedict XVI in 2009, a cordial meeting that nevertheless drew attention to the differences between the church and Obama on abortion.
Several presidents met with popes
To be sure, the relationship between the Obama administration and the Catholic Church is a fraught one. But in Francis, the White House sees the popular pope and his emphasis on economic disparity as a form of moral validation of the president's economic agenda.
"The pope challenges us. He implores us to remember people, families, the poor," Obama said in an interview with the Italian daily Corriere della Sera published ahead of his papal visit. "He invites us to stop and reflect on the dignity of man."
'The pope challenges us. He implores us to remember people, families, the poor.' - U.S. President Barack Obama
Several presidents have found comfort if not allies in the pope.
Former president Ronald Reagan and Pope John Paul II famously shared an antipathy for the former Soviet Union, Reagan the Cold War warrior and the pope a Polish priest who fought communism in his country and later in Europe.
"Sometimes in these meetings there are compatible personalities," said Paul Begala, a former aide to former president Bill Clinton and a Catholic himself. He recalled being with Clinton when the then president met John Paul II in Denver.
"They were only supposed to meet alone for five minutes," he said in an interview earlier this year. "Those two gregarious, charismatic men sat in that room for an hour without another soul in there."
Abortion, health care opinions differ
The Obama-Francis chemistry remains to be seen, but thematically both seem to be on some of the same pages.
Philadelphia Archbishop Charles Chaput, at the Vatican this week trying to secure Francis's attendance in Philadelphia next year, said he expected the Obama-Francis meeting to be good for both the U.S. and the Vatican.
"We have the most important religious figure in the world as part of that meeting, and one of the most important political leaders, so anytime the church and politics come together is an important moment for dialogue, discussion and the commitment to the common good," Chaput told reporters Tuesday at the Vatican.
Still, there are difficult areas of discord between U.S. bishops and the Obama administration over abortion and the administration's health care overhaul. U.S. bishops were among the most outspoken opponents of Obamacare, objecting to its mandatory coverage of contraception. The Supreme Court this week seemed divided when hearing arguments in a case in which companies argued that they have religious rights and can object to such coverage based on such beliefs.
In a possible hint of the Vatican's position, Vatican Radio, in an article in advance of the visit, took special note that Obama's papal audience takes place "in the context of a complex phase of the administration's relations with the Church of the United States." It went on to mention implementation of the health care law and legalization of gay marriage.
On Ukraine, Francis issued an appeal for dialogue early in the month. But otherwise the Vatican has kept a low profile on the issue, a possible sign that it doesn't want to inflame tensions with the Russian Orthodox Church.
Developments in the Middle East are also a likely topic. Obama has opposed military strikes against Syria in favour of diplomacy. And he will travel to Jordan, Israel and the Palestinian territories at the end of May.
Obama won Catholic vote in 2 elections
Francis faithfully backs church teaching on abortion — he has said he's a "son of the church" — but his emphasis and tone are elsewhere. He has said he wants his church to be more of a missionary, welcoming place for wounded souls rather than a moralizing church.
He caused a fuss in November when he decried some conservative economic theories as unproven. "The excluded are still waiting," he wrote.
Francis' attention to poverty has also captured the attention of Republicans, prompting some to stake out high-profile anti-poverty positions. House Speaker John Boehner of Ohio has extended a formal and open invitation to the pope to address Congress when he visits the United States.
No doubt there is a political dimension to Obama's visit as well. The president won the Catholic vote in both of his elections, helped by heavy support from Hispanic Catholics. Some of that support has waned since.
Meanwhile, the Pew Research Centre found that the pope remains hugely popular, with more than eight in 10 U.S. Catholics saying they have a favourable view of the pontiff.