By late Friday morning, President Biden will have met with Pope Francis — marking the 31st time a president has met with the leader of the Catholic Church.
The convergence of the White House and the Vatican is only a tradition that began at the start of the 20th Century under President Woodrow Wilson. Even after Wilson, the next president wouldn't meet face-to-face with the pontiff again until about 40 years later.
"This is really a modern phenomenon," Shaun Casey, a professor in Georgetown University's Walsh School of Foreign Service, told NPR. Casey is also a senior fellow at the university's Berkley Center for Religion, Peace, and World Affairs.
For Biden, whose Roman Catholicism has been a part of his public persona as well as a staple of his personal life, this meeting with Pope Francis will be both personal and formal, according to the White House.
With the Obama administration and now Biden's, "I think they discovered in Pope Francis a very willing partner to address some of these massive global issues like climate change, like refugees," Casey said. "When you see that political policy overlap, you see a deepening of the ties and deepening of the relationship between the two entities. And we are in one of those moments."
But as other historical and theological experts shared with NPR, these meetings have not always had such a significance.
The first meeting didn't happen until 1919
In January of 1919, Woodrow Wilson was on a months-long European trip in the wake of World War I.
"On January 4, Mr. Wilson called upon his Holiness Pope Benedict XV," according to America magazine at the time. Benedict welcomed Wilson "most cordially. They spent about a half hour together. It is not, of course, officially known what subjects they discussed."
Wilson's meeting with the pope, which occurred during a time in which the U.S. harbored major anti-Catholic sentiment, is far different than what the White House's relationship with the Vatican is now.
Such a meeting was seen in the U.S. as "politically fraught," Casey said. "There was no political advantage for a president to meet with a pope at that point."
Reportedly, Wilson wouldn't step away from his face-to-face with the pope fully unscathed. An awkward moment arose when the pontiff offered a papal blessing to the White House's entourage. Wilson declined, but offered up the Catholics among his staff to receive one.
It was after President Dwight D. Eisenhower met with Pope John XXIII at the Vatican that a president meeting with a pope became more normalized and a tradition.
Biden is just the second Catholic president
About one-in-five U.S. adults are Roman Catholic, according to Pew Research Center. Yet, prior to Biden, John F. Kennedy was the only Catholic president to serve.
Former Secretary of State John Kerry, who is now the U.S. special presidential envoy for climate, was the only other Catholic to be listed as a presidential nominee of a major party ticket since Kennedy's assassination in 1963.
The Pew Research Center says historically, about a quarter of presidents – including George Washington, James Madison and Franklin Roosevelt – were members of the Episcopal Church. The second largest group are Presbyterians, with eight presidents, listing that as their denomination.
Kennedy faced anti-Catholic sentiment during his run for the presidency, so his meeting with the pope was closely watched, Seattle University's former dean of the School of Theology and Ministry Mark S. Markuly said.
At the time, many Americans thought Kennedy, as a Catholic, would have competing loyalties to the Vatican and to the United States, he said.
The first papal visit to the White House was in 1979
Once meetings with the pope became more normalized, the pontiff eventually made his way to the U.S. — but it's been a rare occurrence.
On Oct. 6, 1979, Pope John Paul II became the first pope to visit the White House. He arrived in style — in an open-topped limousine — and met with then-President Jimmy Carter.
"The people of our country have waited a long time for this meeting," Carter said at the time.
The second pope to stop by 1600 Pennsylvania Avenue was Pope Benedict XVI, who visited the White House on April 16, 2008 — also the pontiff's 81st birthday, according to the White House Historical Association. President George W. Bush and first lady Laura Bush surprised the pope with a birthday cake before meeting privately.
And on Sept. 23, 2015, Pope Francis became the third pontiff in history to pay a visit to the White House under the Obama administration.
Under Reagan, the dynamic changes
Carter's meeting with Pope John Paul II helped launch a diplomatic relationship between the U.S. and the Vatican — one that President Ronald Reagan would build off of.
Reagan saw a kindred spirit in the pope when it came to fighting the threat of communism during the 1980s, according to Matt Dallek, a political historian and professor of political management at George Washington University.
The pope at the time, who lived in communist-era Poland and under Nazi rule, was a staunch anti-communist. He supported the Polish Solidarity Movement, which is widely seen as having a major role in ending Communist rule in Poland.
"Reagan and the pope really shared that sensibility," Dallek said. "Certainly the meeting with the pope, and I think, the alignment with the pope politically was helpful."
In 1984, the U.S. formally recognized and exchanged ambassadors with the Holy See.
It wasn't always smooth sailing
John Paull II was a strong critic of the war in Iraq — an issue that made some awkward moments with President George W. Bush.
When Bush last met with the pope at the Vatican in June 2004, the pope urged a quick return to sovereignty for Iraq and took a moment to criticize the ongoing war there.
And former President Donald Trump's relationship with Pope Francis was far more tense than his predecessor's.
During the 2016 campaign, Francis took what was seen as a hit at Trump by criticizing the future president's view on building a wall in Mexico. Francis said those who want to build walls instead of bridges are "not Christian."
Trump later responded, criticizing the pontiff's comments and suggested Francis was a "pawn" for Mexico.
Once the two met in person, images of the pontiff frowning while standing next to Trump became a punchline.
Georgetown's Casey, said Biden's meeting with Pope Francis is important following the Trump presidency.
"Biden is actually repairing a fractured diplomatic relationship," he said. This meeting and what's said will be "a signal to the Vatican that you have a partner now in the White House."