(CNN)Imagine this split screen: On one side is Donald Trump, repeating his campaign pledge to build a big wall between the United States and Mexico. On the other is Pope Francis, kneeling to pray for the thousands of undocumented immigrants who have died trying to cross the border.
The Pope, 'The Donald' and the wall between them
As the Pope visits Mexico through February 17, he is not expected to tussle with Trump or directly criticize U.S. immigration policy. Papal aides said Francis wants to avoid appearing to intervene in the presidential election.
That hasn't stopped Trump from taking aim at the Pope.
"I think that the Pope is a very political person. I think that he doesn't understand the problems our country has," Trump said in an interview Thursday on Fox Business. "I don't think he understands the danger of the open border that we have with Mexico."
Will Francis fire back? Not likely. But Catholic leaders say the pontiff will send an unmistakeable message when he travels to the border in Juarez, Mexico, on Wednesday.
"He will be calling on us to look with compassion on a group of people who have suffered terribly," said Bishop Mark Seitz of El Paso, Texas, a city that sits across the Rio Grande from Juarez. "And perhaps that will lead people to seek out some different solutions than are now being proposed."
Francis has already spoken out against impenetrable international borders, calling them "monuments of exclusion" and even a "form of suicide" that closes countries in on themselves. He has also urged the United States and Mexico to protect Central American migrants, particularly children, seeking to escape poverty and violence.
It is unclear, though, whether American Catholics are heeding the Pope's message.
Half of Catholics in the United States say they agree with Francis on immigration, according to a survey conducted by the Public Religion Research Institute. But a majority of conservative Catholics (54%) say that Trump, whose signature issue is buttressing the border between the United States and Mexico, would make a "good or great" president, a Pew poll found.
And in a strange bit of statistical symmetry, the exact same percentage of Americans (5%) named the billionaire businessman and famously no-fuss Francis as the man they most admired in 2015, according to Gallup.
But the politics of immigration extend well past the campaign trail.
The Pope's trip to Mexico comes weeks after the Supreme Court -- five of whose justices are Catholics following the death of Antonin Scalia on Saturday -- agreed to hear a challenge to President Barack Obama's plan to protect millions of undocumented immigrants from deportation. And just last month, the Justice Department announced plans to repatriate some of the 313,000 people who crossed the border illegally last year.
"I don't think the Holy Father's trip to Juarez is political," said the Rev. Timothy Kesicki, president of the U.S.-based Jesuit Conference. "But how could it not have political overtones? It's going to be drawing a lot of attention to immigration at a time when we are having debates about it."
Still, it would be a mistake to view the Pope's Mexican visit solely through an American or political lens, Kesicki and other Catholics said. Mexico is a big, complicated country with far more than immigration and El Norte on its mind.
For his part, Francis told Mexican schoolchildren that he is not coming to their country "as a Magi king" bearing messages, ideas and solutions.
"I am going there to receive the best of you, and to pray with you that the problems of violence, corruption and all that you know is happening can be resolved."
Here are some of the big themes the Pope is expected to address in his five days in Mexico:
On his way to Mexico, Francis stopped in Cuba for several hours, where he held a historic meeting with the head of the Russian Orthodox Church, Patriarch Kirill.
It was the first time a pope and a Russian patriarch have ever met, and a significant step toward rebuilding relations between Catholics and Orthodox Christians, who separated nearly 1,000 years ago after the Great Schism. (Also called the East-West split, the fight was mostly over theology and the primacy of the pope. In the end, the pope and the patriarch excommunicated each other.)
Francis and Kirill spent a three hours together at Jose Marti International Airport in Cuba before signing a joint declaration. Delicately dancing around centuries of theological tensions, declaration pleaded for world leaders to protect persecuted Christians.
"Thousands of victims have already been claimed in the violence in Syria and Iraq, which has left many other millions without a home or means of sustenance."
Francis and Kirill touted their historic conclave as an "indispensable" example of civility for a world riven by violence, poverty and sectarian strife.
The meeting was a diplomatic victory for Francis, who has made door-opening dialogue a prominent feature of his foreign policy.
But it also carried some risks. Critics have warned that Kirill and Russian President Vladimir Putin, who are close, will use the Pope to boost their profile among Orthodox Christians and popularity in the West.
Despite decades of Soviet-style repression during the 20th century, Catholicism survived and even thrived in Mexico. It now boasts 122 million Catholics, second only to Brazil in size.
Paradoxically, though, as the long-ruling Institutional Revolutionary Party lifted some restrictions on Catholicism, the church lost some of its religious monopoly. While 90% of Mexicans were raised Catholic, according to a 2014 Pew report, 81% currently identify as such, a small but significant drop.
Francis will take some steps to stanch the bleeding, visiting Chiapas, for instance, where Protestant churches have flourished. There, on February 15, the Pope is expected to issue a decree allowing indigenous people to celebrate Mass in their local languages. He may also apologize for historical wrongs done in the name of the church, as he did during a trip to Bolivia last year.
Some Catholics say the Pope may also seek to atone for the sexual abuse perpetrated by Marcial Maciel Degollado, the disgraced founder of the Legion of Christ who sexually abused seminarians and fathered several children. Degollado, who died in 2008, was a powerful figure in the Mexican church for decades.
"It will be the first time a pope has been in Mexico since that blew up," said Kesicki. "That's another flashpoint that I think he may have to address."
And while staying each night in Mexico City, the "Pope of the peripheries" will travel via helicopter to several cities that have never seen a pontiff in person, even during Saint John Paul II's five trips to Mexico.
Tracing the path of many migrants, Francis will travel from Chiapas in the far south, where as many as 150,000 Central Americans enter Mexico each year, to Juarez in the north, where many hope to enter the United States.
"Those are two very wounded spots," said Bishop Daniel Flores of Brownsville, Texas, who is one of two U.S. bishops who will be part of the papal entourage in Mexico.
"He wants us to be aware that those are human wounds and we cannot be indifferent to them."
In 2014, Francis went to the mafia's heartland in southern Italy and told mobsters that, because of their "evil ways," they are "excommunicated from the church." It was the first time a pope has booted the mafia from the flock, and established Francis as a man unafraid of calling out crime bosses.
Many Catholics expect the Pope to deliver a similar message next week in Mexico, particularly in Morelia in Michoacan, a state ravaged by cartels that often adopt the trappings of religion to sanctify their violence. The main Michoacan cartel, for instance, calls itself the Knights Templar, copying the name of a Catholic order of medieval Crusaders.
"He's not afraid to say what he thinks people need to hear," said Flores, the Brownsville bishop. "He can say things that some of our politicians are unable, or unwilling, to say."
Francis may temper his criticism with a bit of tough love. In announcing his "Year of Mercy" last April, he said that God's grace is open even to mobsters.
"I direct this invitation to conversion even more fervently to those whose behavior distances them from the grace of God," the Pope said.
"I particularly have in mind men and women belonging to criminal organizations of any kind. For their own good, I beg them to change their lives."
Whether it's stopping for an impromptu prayer at the barrier separating Bethlehem from Jerusalem or celebrating Mass on an altar made of migrants' boats, Francis has shown a fondness for grand geopolitical gestures.
The point, he often says, is to prick the conscience of a world often apathetic about the plight of the poor and the marginalized.
In Mexico, the Pope will again visit "places of pain," as he calls them, including a children's hospital in the capital city and a notorious prison in Juarez, a city once known as the "murder capital of the world."
But the moment many Catholics are most eagerly awaiting will come when the Pope approaches the U.S.-Mexico border in Juarez.
Papal aides say security and logistical barriers will prevent the Pope from making a political point by crossing the border. But he will come as close as he can, standing just 50 yards from El Paso. Across the river and through the fences, a group of "Francis VIPs," including undocumented immigrants seeking asylum in the United States, await the Pope's blessing.
"These are the people the Pope has come to see and pray for," said Seitz, the El Paso bishop who organized the event.
Francis is expected to say a prayer at the border fence and lay flowers in memory of the more than 6,000 migrants found dead on the U.S. side of the border between 1998 and 2013, according to U.S. Border Control estimates.
"The symbolism of this moment will not be missed by anyone in the border region," said Joe Boland, vice president of missions at Catholic Extension, a charity with a long history in the area. "It will be like the Pope coming to Ellis Island."
Later on February 17, the Pope will celebrate a large Mass not far from the border, where migrants and victims of drug violence will be among the 200,000 receiving Holy Communion.
Across the Rio Grande, the Diocese of El Paso will host pilgrims from as far away as Brooklyn and Miami who will watch a livestream of the papal Mass in Sun Bowl Stadium.
"We want to demonstrate to the Holy Father that our two nations, and our two sister cities, embody 'Two Nations, One Faith,' " said Seitz.
While the World Health Organization has declared the Zika virus a public health emergency, the Pope isn't likely to address the dangerous virus in Mexico, though infected mosquitoes have been reported there.
But with several South American countries advising women to avoid getting pregnant in order to prevent possible birth defects that can result from Zika, Catholics are in a tough theological spot.
The church counsels against most forms of birth control, and even though surveys show many South American Catholics ignore such teachings, the Pope will likely be wary of weighing in before all the facts about Zika are known.
If Francis does address the virus and the church's position on birth control, it will likely be during the post-trip press conference on the flight from Mexico back to Rome. And, as reporters know, when this Pope approaches a microphone, he often makes news.
He may even address a certain billionaire businessman.