Some of the United States’ most prominent Catholic bishops will make a dramatic pastoral visit Monday, when they will minister at a detention center on the U.S.-Texas border to migrant children separated from their parents.

The unusual high-profile visit by the top spiritual leaders aims to draw attention to unresolved questions around immigration and around the treatment of migrants. Yet there will be no cameras when the clerics pray with the separated children, no audiotapes.

That’s because the bishops, who arrived for the two-day fact-finding mission Sunday, are walking a fine line among their divided flock on the topic of immigration. American Catholics, like Americans overall, are divided about immigration policy. And 2018 is a time when Americans’ deference to institutional leaders of any stripe is already thin.

Which means bishops of the Catholic Church who want to affect policy are being cautious. Telling immigration reform activists not to carry signs. Don’t use the word “protest.” And when you come to the border to make a point, do it primarily through prayer.

On Sunday, when the fact-finding mission began, that meant Mass in the San Juan Basilica, where the service is celebrated with the accompaniment of a 12-piece mariachi band. But behind the celebratory music was powerful symbolism: The shrine is renowned as a pilgrimage site for migrants. The worship was dedicated to migrant children separated from their families.

“The bishops are visiting here with us to understand better what an immigrant lives—a mother, a child, a family. And then to respond,” said Bishop Daniel Flores, of the local Brownsville diocese, which adjoins the Mexican border. “As a church, we have to be the ones who say ‘there’s always a human face, and the human face always points to Christ in whatever suffering there is.’ If we don’t stand up and say this, who is going say it?”

The delegation of around a half-dozen bishops is led by Cardinal Daniel DiNardo, the president of the United States Conference of Catholic Bishops. In addition to worship at the detention center, the clerics will visit a humanitarian respite center that has provided meals, shelter, clean clothes, and medical and mental health care to more than 100,000 migrants, mostly from Central America, since 2014.

The bishops are scheduled to report on their findings at a press conference on Monday night here in San Juan.

Such a visit by so many high-level bishops to the border is very unusual. The last time a similar trip was organized, in 2014, a group led by Cardinal Sean O’Malley, of Boston, made international headlines by distributing communion through sections of border fence. Four years later, in a much different political landscape, observers are asking if the new delegation will have the same galvanizing effect and will influence policy on issues such as the fate of the 2,000 children who remain separated from their parents, and the Trump Administration’s proposal to indefinitely detain families with children at military bases.

Until now, even as family separation has dominated headlines, the bishops have adopted a relatively cautious tone, condemning the recent zero-tolerance policy while steering clear of endorsing or opposing specific laws, and emphasizing that Catholics can disagree on immigration policy.

“There’s a divide in the church,” says Kevin Appleby, director of policy at the Center for Migration Studies, a Catholic thinktank. “[The bishops] not only want to influence the administration, but also politically conservative Catholics who otherwise would oppose immigration. The question is how directly they will confront the president, since they are allies with him on pro-life and other socially conservative issues. And can they influence those Catholics who voted for Trump and motivate them to speak out against this policy?”

The choice of the basilica, which overflowed beyond the 1,800-person capacity for the bishops’ mass, was full of symbolism. Behind the altar, carved figures of migrant workers and their families surrounded a three-foot statue of Our Lady of San Juan del Valle, a figure that is reputed to have healing powers and  draws thousands of pilgrims each year. The site was also home to masses, in the 1960s, held with Cesar Chavez in support of striking migrant workers.

As they gathered on the basilica’s steps after the mass, local parishioners expressed hope that the bishops’ visit could move hearts and minds beyond the border.

“As Catholics, we believe in keeping all the families together,” said Pamela Rodriguez, 27, a home health nurse who attended mass with her two children, ages nine and 10. “I believe that God is very strong, and that he can open up the eyes of any and every person. Sometimes it just takes the voice of certain individuals to break through.”

One specific policy issue the bishops want to be addressed is the Trump Administration’s proposal to indefinitely house immigrants in family detention centers, many at military bases. “We really have to keep our eye on the developing situation—to see how families are going to be housed,” Bishop Flores told the Post. “Part of the delegation, I hope, is the chance to really ask some questions about how this is going to unfold, so that we’re prepared for it.”

Border bishops have been among the most outspoken in condemning the Trump Administration’s zero tolerance policy. The Catholic Church has also played a leading role in receiving refugees at the border once they’re released from detention.

“The community has gathered together to make sure that we take care of these families, and that we welcome then,” Sister Norma Pimentel, the executive director of Catholic Charities of the Rio Grande Valley, said after the Mass. Pimentel runs the Humanitarian Respite Center in McAllen, a few miles west of here, which the bishops visited. “We must offer compassionate and humane processes that care for these families who are victims of structures that are corrupt and abusive in their home countries.”

But even on the border, Catholic leaders have eschewed anything that might be labeled activism, even as tens of thousands of protestors take to the streets nationwide. At an interfaith prayer vigil for separated families in McAllen, organized by the Brownsville diocese last week, gatherers marching from a park to the federal courthouse were asked not to carry signs or chant. They were explicitly instructed that the religious event was not a protest.

Nationally, the Catholic Church seems to be walking an even more careful line on immigration, at least publicly.

Bishops have held several events in recent years on the border, normally with just a few clerics, and a tone that is general and spiritual – such as celebrating Mass to honor border-crossers who died, or condemning conditions at detention centers. They don’t often advocate for specific policy goals or laws to pass or defeat.

In addition to the highly-publicized border mass with Cardinal O’Malley, in 2014, Pope Francis prayed on the Mexico side of the border in 2016. Bishops from Mexico and California also prayed together on either side of the border last month, the Times of San Diego reported.

Unlike other faith groups on the border, the bishops have been careful not to sound politically confrontational.

Some church leaders in the U.S. and Rome have for decades been wary about explosive church activism. A movement that gained steam in the Latin American church in the 1960s and 1970s called liberation theology, called for Catholics to fight poverty not just through prayer but through systemic change – even revolution. In the U.S. the bishops pushed back against Catholic activists who protested the Vietnam War.

U.S. Catholics mirror the general public in their views on immigration. A May poll found that about half of Catholics say the U.S. has a responsibility to accept refugees – the same as the general public.

Some are pushing at the edges. Tucson Bishop Edward Weisenburger last month at an annual meeting of  bishops suggested the possibility of spiritual penalties for Catholics involved in separating children from their families at the border.

“Canonical penalties are there in place to heal, and therefore, for the salvation of these people’s souls. Maybe it’s time for us to look at canonical penalties,” Weisenburger said in his remarks to the meeting, the Religion News Service reported.

Some Catholics applauded Weisenburger, noting some bishops have withheld communion from Catholic politicians who support abortion rights. Others said such penalties shouldn’t be toyed with in the political arena.

It’s unclear where such outspoken attitudes fit in the church’s immigration strategy. Since Weisenburger spoke out he hasn’t commented much in public. His office didn’t promptly return calls for comment for this piece.