(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.

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.

Photos: Pope Francis visits Mexico Photos: Pope Francis visits Mexico Pope Francis prays next to the U.S. border before celebrating Mass in Ciudad Juarez, Mexico, on Wednesday, February 17. The Pope's five-day trip to Mexico started on February 12. Hide Caption 1 of 33 Photos: Pope Francis visits Mexico Pope Francis receives a cross made by an inmate at a prison in Ciudad Juarez on February 17. Hide Caption 2 of 33 Photos: Pope Francis visits Mexico Altar boys cheer as the Pope arrives in Ciudad Juarez on February 17. Hide Caption 3 of 33 Photos: Pope Francis visits Mexico Pope Francis pays his respects to Jose Sanchez del Rio at a cathedral in Morelia, Mexico, on Tuesday, February 16. Jose, 14, was killed by government officials in 1928 after he refused to renounce his Catholic faith. Hide Caption 4 of 33 Photos: Pope Francis visits Mexico Nuns attend a Mass with Pope Francis at a stadium in Morelia on February 16. Hide Caption 5 of 33 Photos: Pope Francis visits Mexico Pope Francis celebrates Mass in Morelia on February 16. Hide Caption 6 of 33 Photos: Pope Francis visits Mexico The Pope waves to a crowd in San Cristobal de las Casas, Mexico, on Monday, February 15. Hide Caption 7 of 33 Photos: Pope Francis visits Mexico Thousands of indigenous Mexicans flocked to a field in San Cristobal de Las Casas to celebrate Mass with Pope Francis on February 15. Hide Caption 8 of 33 Photos: Pope Francis visits Mexico Indigenous women attend Mass in San Cristobal de las Casas. Hide Caption 9 of 33 Photos: Pope Francis visits Mexico Pope Francis walks with the pastoral staff during Mass in Ecatepec -- a rough, crime-plagued Mexico City suburb -- on Sunday, February 14. Hundreds of thousands of people gathered for Mass there. Hide Caption 10 of 33 Photos: Pope Francis visits Mexico Catholic faithful attend Mass in Ecatepec. Hide Caption 11 of 33 Photos: Pope Francis visits Mexico Pope Francis waves from his "Popemobile" on his way to take a helicopter to Ecatepec. Hide Caption 12 of 33 Photos: Pope Francis visits Mexico Pilgrims wave flags as they wait for Pope Francis to arrive in Ecatepec on February 14. Hide Caption 13 of 33 Photos: Pope Francis visits Mexico Dancers perform in Ecatepec before the arrival of Pope Francis on February 14. Hide Caption 14 of 33 Photos: Pope Francis visits Mexico Pope Francis celebrates Mass at the Basilica of Our Lady of Guadalupe on Saturday, February 13. The basilica in Mexico City is considered the largest and most important Marian shrine in the world. Hide Caption 15 of 33 Photos: Pope Francis visits Mexico Pope Francis greets a child as he walks in procession at the Basilica of Our Lady of Guadalupe. Hide Caption 16 of 33 Photos: Pope Francis visits Mexico Prelates wait for the arrival of Pope Francis at the Basilica of Our Lady of Guadalupe. Hide Caption 17 of 33 Photos: Pope Francis visits Mexico Pope Francis, reflected in the frame that holds the image of the Virgin of Guadalupe, holds a bouquet of flowers as he prays to her inside the basilica built in her honor. Hide Caption 18 of 33 Photos: Pope Francis visits Mexico Pope Francis meets with bishops during his visit to the national cathedral in Mexico City on February 13. The Pope demanded that Mexican bishops challenge the "insidious threat" posed by the drug trade. Hide Caption 19 of 33 Photos: Pope Francis visits Mexico Pope Francis is recognized as a distinguished guest by Mexico City Mayor Miguel Angel Mancera on February 13. Hide Caption 20 of 33 Photos: Pope Francis visits Mexico Pope Francis waves to the crowd in Mexico City's main square, the Zocalo, on February 13. Hide Caption 21 of 33 Photos: Pope Francis visits Mexico Pope Francis kisses a child in the Zocalo on February 13. Hide Caption 22 of 33 Photos: Pope Francis visits Mexico Pope Francis dons a Mexican sombrero on February 13. Hide Caption 23 of 33 Photos: Pope Francis visits Mexico Pope Francis arrives in Mexico City's main square on February 13. Hide Caption 24 of 33 Photos: Pope Francis visits Mexico Pope Francis kisses a child in a wheelchair on February 13. Hide Caption 25 of 33 Photos: Pope Francis visits Mexico People wave to Pope Francis as he makes his way to Mexico City's main square. Hide Caption 26 of 33 Photos: Pope Francis visits Mexico Pope Francis laughs with Mexican President Enrique Pena Nieto during a welcome ceremony at the National Palace. Hide Caption 27 of 33 Photos: Pope Francis visits Mexico Pope Francis is welcomed by Pena Nieto and his wife, Angelica Rivera, on February 13. Hide Caption 28 of 33 Photos: Pope Francis visits Mexico A woman holds an Uruguayan flag while she waits along the route that Pope Francis would take to Mexico City's main square. Hide Caption 29 of 33 Photos: Pope Francis visits Mexico Pope Francis greets youth dressed in traditional outfits as he's escorted by Pena Nieto and first lady Angelica Rivera on Friday, February 12. Hide Caption 30 of 33 Photos: Pope Francis visits Mexico A group of children runs to embrace the Pope during his welcoming ceremony in Mexico City on February 12. Hide Caption 31 of 33 Photos: Pope Francis visits Mexico Pope Francis waves to people as he arrives to the Vatican's diplomatic mission in Mexico City on February 12. Hide Caption 32 of 33 Photos: Pope Francis visits Mexico Pope Francis arrives at Benito Juarez International Airport in Mexico City on February 12. Hide Caption 33 of 33

"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:

From Russia with love?

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 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.

A Mexican monopoly

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."

Excommunicate the cartels?

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."

Mexico's 'Ellis Island'

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.

JUST WATCHED A new generation tries to reinvent old Juarez Replay More Videos ... MUST WATCH A new generation tries to reinvent old Juarez 03:42

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.

Zika

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.

Photos: Zika virus outbreak Photos: Zika virus outbreak A pest control worker fumigates a school corridor on the eve of the annual national Primary School Evaluation Test in Kuala Lumpur on Sunday, September 4. Malaysia reported its first locally transmitted Zika case on September 3. Hide Caption 1 of 29 Photos: Zika virus outbreak A banner about Zika virus is seen as ferry passengers arriving from Singapore get in line at the immigration check on September 4, in Batam, Indonesia. Hide Caption 2 of 29 Photos: Zika virus outbreak A banner is flown over the South Pointe Park area, Tuesday, September 6, in Miami Beach, Florida. Hide Caption 3 of 29 Photos: Zika virus outbreak A pest control worker fumigates drains at a local housing estate where the latest case of Zika infections were reported on Thursday, September 1, in Singapore. Hide Caption 4 of 29 Photos: Zika virus outbreak Florida Gov. Rick Scott and Florida Surgeon General Dr. Celeste Philip address the media gathered at the Miami-Dade County Department of Health as they announce five cases of Zika in a 1.5 mile area of Miami Beach on Friday, August 19, in Miami, Florida. Hide Caption 5 of 29 Photos: Zika virus outbreak Brazil's interim President Michel Temer, center right, meets with officials during Temer's first visit to the Olympic Park on Thursday, June 14, in Rio de Janeiro. The Rio 2016 Olympic Games commence August 5 amid a political and economic crisis in the country along with the Zika virus outbreak. Hide Caption 6 of 29 Photos: Zika virus outbreak Rio 2016 Chief Medical Officer Joao Grangeiro, Municipal Secretary of Health Daniel Soranz and Sub-secretary of the State for Health and Surveillence Alexandre Chieppe field questions from the media during an International Media Briefing to address the Zika virus on Tuesday, June 7, in Rio de Janeiro. Hide Caption 7 of 29 Photos: Zika virus outbreak A health worker fumigates an area in Gama, Brazil, to combat the Aedes aegypti mosquito on Wednesday, February 17. The mosquito carries the Zika virus, which has suspected links to birth defects in newborn children. The World Health Organization expects the Zika outbreak to spread to almost every country in the Americas. Hide Caption 8 of 29 Photos: Zika virus outbreak A man places a mosquito net over a bed at a home for the elderly in Masaya, Nicaragua, on Thursday, February 11. Hide Caption 9 of 29 Photos: Zika virus outbreak An Aedes aegypti mosquito floats in stagnant water inside a tire at a used tire store in Villavicencio, Colombia, on Thursday, February 4. Hide Caption 10 of 29 Photos: Zika virus outbreak A health worker fumigates an area in Caracas, Venezuela, on Tuesday, February 2. Hide Caption 11 of 29 Photos: Zika virus outbreak A lab worker exposes his arm to Aedes aegypti mosquitoes during testing at the Roosevelt Hospital in Guatemala City, Guatemala, on Monday, February 1. Hide Caption 12 of 29 Photos: Zika virus outbreak Tainara Lourenco sits inside her home in Recife, Brazil, on Friday, January 29. Lourenco, five months pregnant, lives at the epicenter of Brazil's Zika outbreak. The Zika virus has been linked to microcephaly, a neurological disorder that results in newborns with small heads and abnormal brain development. Hide Caption 13 of 29 Photos: Zika virus outbreak Dr. Angela Rocha shows brain scans of a baby born with microcephaly at the Oswaldo Cruz Hospital in Recife on Thursday, January 28. Hide Caption 14 of 29 Photos: Zika virus outbreak Alice Vitoria Gomes Bezerra, a 3-month-old baby with microcephaly, is placed in her crib by her father Wednesday, January 27, in Recife. Hide Caption 15 of 29 Photos: Zika virus outbreak A health ministry employee fumigates a home in Soyapango, El Salvador, on January 27. Hide Caption 16 of 29 Photos: Zika virus outbreak A lab technician at the Oswaldo Cruz Foundation Institute stores Aedes aegypti mosquitoes to be used in research in Recife on January 27. Hide Caption 17 of 29 Photos: Zika virus outbreak A patient suffering from Guillain-Barre syndrome recovers at a hospital in San Salvador, El Salvador, on January 27. Researchers are looking into a possible link between Zika and Guillain-Barre, a rare disorder that causes the body's immune system to attack its nerves. Hide Caption 18 of 29 Photos: Zika virus outbreak Luiz Felipe lives in Recife and is one of more than 4,000 babies in Brazil born with microcephaly since October. The drought-stricken impoverished state of Pernambuco has been the hardest-hit, registering 33% of recent cases. Hide Caption 19 of 29 Photos: Zika virus outbreak A health worker sprays insecticide under the bleachers of Rio de Janeiro's Sambadrome on Tuesday, January 26. Hide Caption 20 of 29 Photos: Zika virus outbreak A Brazilian soldier inspects a home in Recife on Monday, January 25, while canvassing the neighborhood and attempting to eradicate the larvae of mosquitoes linked to the virus. Hide Caption 21 of 29 Photos: Zika virus outbreak David Henrique Ferreira, a 5-month-old who has microcephaly, is watched by his brother in Recife on January 25. Hide Caption 22 of 29 Photos: Zika virus outbreak The larvae of Aedes aegypti mosquitoes are photographed in a lab in Cali, Colombia, on January 25. Scientists are studying the mosquitoes to control their reproduction and resistance to insecticides. Hide Caption 23 of 29 Photos: Zika virus outbreak Angelica Prato, a pregnant woman infected by the Zika virus, receives medical attention at a hospital in Cucuta, Colombia, on January 25. Hide Caption 24 of 29 Photos: Zika virus outbreak A woman walks through fumes as health ministry employees fumigate an area in Soyapango on Thursday, January 21. Hide Caption 25 of 29 Photos: Zika virus outbreak Brazilian soldiers apply insect repellent as they prepare for a cleanup operation in Sao Paulo on Wednesday, January 20. Hide Caption 26 of 29 Photos: Zika virus outbreak A researcher at the University of Sao Paulo holds a container with female Aedes aegypti mosquitoes on Monday, January 18. Hide Caption 27 of 29 Photos: Zika virus outbreak A graveyard in Lima, Peru, is fumigated on Friday, January 15. Hide Caption 28 of 29 Photos: Zika virus outbreak Aedes aegypti mosquitos are seen at the University of Sao Paulo on January 8. Researchers from the Pasteur Institute in Dakar, Senegal, came to Brazil to train local researchers to combat the Zika virus epidemic. Hide Caption 29 of 29

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.