Vice President JD Vancewitnessed the end of one papacy whenhe visited Pope Francis on Easter Sundayshortly before thepontiff's death. Now, less than a month later, Vance will be present for the beginning of another as he again travels to Rome, this time for the May 18 inaugural mass ofPope Leo XIV. It's a moment to celebrate thenew leader of 1.4 billion Catholics. The "solemn liturgy" in St. Peter's Basilica and Square marks the "official beginning ofPope Leo XIV's pontificate," according to the Vaticannewssite. Vance will be watching with Secretary of State Marco Rubio, their wives and world leaders. For Trump and his team, the trip also could set the tone for the administration's relationship with the Vatican, which wasstrained under Francis. Related:VP Vance prays for Pope Francis, turns cheek on political disputes "It was a difference of principles," said Duke theology professor Peter Casarella. Trump and Francisrepeatedly clashedover immigration. Francis became pope in 2013 and spoke out when Trump was first running for president in 2016 and pledged to build a wall on the southern border. "A person who only thinks about building walls, wherever they may be, and not about building bridges, is not a Christian," Francis said at the time. This year, Francis said of Trump's mass deportation plan on the eve of his inauguration: "If it is true, it will be a disgrace." Francis also was astrong advocatefor tackling climate change, which Trump has called a "hoax." Trump fired back at Francis in 2016, saying: "For a religious leader to question a person's faith is disgraceful." Whether his relationship with Leo will be different remains to be seen, but the new pope seems to share Francis' views. Leo said the dignity of migrants should be respected in hisfirst address to world diplomatsMay 16. Those who knowthe new pope say he is committed to social justice and helping migrants. Casarella said when it comes to the church's position on migrants, "the lines are drawn, they can't change." That could mean more friction with the Trump administration under Leo. Leo shared criticism of Vance and Trump on social media prior to becoming pope. On April 14, Leo retweeted criticism of Trump and El Salvadoran President Nayib Bukele's response to the Tcontroversialdeportation of El Salvadoran national Kilmar Abrego Garcia, a resident of Maryland. A decade earlier, Leo shared a 2015 column on X, then Twitter, written by a fellow cardinal with the headline "WhyDonald Trump's anti-immigrant rhetoric is so problematic." Leo also shared opinion articles critical of Vance's interpretation of Scripture and immigration. "JD Vanceis wrong: Jesus doesn't ask us to rank our love for others," one headline posted Feb. 3 reads. "There's a long-standing disagreement betweenVice President Vanceand the papacy about how to interpret Catholic teaching," Casarella said. Asked about the dynamic between Vance and the new pope, the vice president's office referred to a social media post he put out on May 8congratulating Leo. More:Who is the new pope? See Pope Leo XIV's first appearance as head of the Catholic Church "I'm sure millions of American Catholics and other Christians will pray for his successful work leading the Church. May God bless him!" Vance wrote. Trump also has expressed warm wishes for Leo. His administration brushed off the pope's past social media activity. "I think it was a surprise to everyone," White House press secretary Karoline Leavitt said of Leo's social media posts. "But it's a great thing for the United States of America and for the world," she said of the first U.S.-born pope, "and we are praying for him." Whether Leo continues to weigh in on American politics will be closely watched. A Chicago native, he is the first U.S. pope and there has been intense interest in America in his appointment. He is likely to visit the U.S. in the first few years of his papacy, Casarella said, and could make many trips to the country. The dynamic between the Trump administration and Leo is not the only source of potential tension on the trip. Rubio is a potential Vance rival for the 2028 GOP presidential nomination. Trump stoked the rivalry talk in arecent interviewwhen he named both Vance and Rubio as potential successors in the Oval Office. Vance dismissed the idea that Trump is creating tension between him and Rubio. "Not all,"he told Fox News."Marco's probably my best friend in the administration. We hang out and talk all the time. He's doing a really good job." Vance and Rubio are the two most prominent Catholics in Trump's administration and his leading surrogates on foreign affairs. They are logical choices to represent Trump at the mass said Joel Goldstein, a St. Louis University professor who studies the vice presidency. Because both men are considered leading contenders for the 2028 GOP presidential nod, the trip also has "possible political resonance" though, Goldstein added. Yet each has made their Catholic faith a big part of their political identity, and that likely would continue if they run for president, making their first trip to see the new pope a potential touchstone in any future campaign. "This is an old story about politicians who are Catholic using their faith or expressing their faith, and they should," said Casarella, adding: "This might be a prelude to something that's coming up later." Vance's trip continues a strip of high-profile foreign visits in recent months, including astop in Greenlandas Trump talks about acquiring the Danish territory and anappearance in Munichwhere he blasted European officials on their home turf. Contributing: Joey Garrison, Francesca Chambers, Reuters This article originally appeared on USA TODAY:Trump sends Marco Rubio and JD Vance for Pope Leo's inaugural mass