ROME – One of them has made the cover of virtually every magazine in the Western world for preaching about bridges and the human family. The other has reached the presidency of the world’s most powerful country, on the promise of building a border wall between the United States and Mexico.

Both promise reform, both are outsiders from the systems they were chosen to lead, and both have an extremely loyal following and an extremely fierce opposition.

In one corner sits Pope Francis, an 80-year-old Argentinian, head of one of the world’s smallest states but also religious leader of the 1.3 billion Catholics around the world. On the other sits the 70-year-old millionaire businessman turned president, Donald Trump, commander-in-chief of the world’s largest army.

The two will meet for the first time on Wednesday, and although both have recently tried to tone down the rhetoric, there’s a fact that remains: Francis is the first pope in modern history to call out a U.S. candidate for the presidency during the campaign.

It happened in February 2016, during the pope’s flight back from Mexico, mere hours after visiting Ciudad Juarez, a city in the northern Mexican border, where he’d lamented the “human tragedy” of immigration.

At the time, Trump was nothing more than one of a few Republicans still going strong in the primaries, but his buoyancy and campaign promises (though some perceived them as threats), were landing headline after headline.

Journalists traveling with the pope asked him about Trump, and his proposed wall.

“Building walls instead of bridges is not Christian; this is not in the Gospel,” the pope said.

Francis said he hadn’t heard about Trump’s plan, but took reporters’ word for it, and said he’d give Trump “the benefit of the doubt.” But he added: “I’d just say that this man is not Christian if he said it this way.”

Trump responded to the comments, saying it was “disgraceful” for a religious leader to question another person’s faith.

“I am proud to be a Christian and as president I will not allow Christianity to be consistently attacked and weakened, unlike what is happening now,” the president said at the time.

Granted, journalists only ever asked Francis about Trump, never about the competition, so it remains unknown what he would have said about the Democratic candidate, Hillary Clinton. Last October, during one of the presidential debates, both candidates were asked about abortion.

The message Clinton gave was loud and clear: “I will defend Roe v. Wade,” she said, “and I will defend women’s rights to make their own healthcare decisions.”

However, what was said about Trump was said, and the American president, snubbed by the Argentine pope, now comes knocking on his door for a meeting that, even if the two hit it off right away, will still be short: It’s scheduled to begin at 8:30 AM Rome time, and Francis is expected in St. Peter’s Square for the weekly Wednesday audience at about 9:30.

Something often overlooked about that famous February 2016 clash is the fact that Pope Francis was asked about Trump as a reaction to comments made by the then presidential-hopeful, who said he suspected that the pope was being manipulated by the Mexican government, and called the pontiff “a very political person.”

“I think he doesn’t understand the problems our country has,” Trump said at the time. “I don’t think he understands the danger of the open border that we have with Mexico. I think Mexico got him to do it because Mexico wants to keep the border just the way it is because they’re making a fortune and we’re losing.”

The pope responded by saying he was thankful of being called a politician, because “Aristotle defined the human person as animal politicus … At least I am a human person!”

Although this is perhaps the most memorable exchange between the two, there have been others.

For instance, never-forgiving Twitter reveals that before he decided to run for the presidency, Trump was a supporter of Pope Francis:

Though he also expressed his differences with Francis’s humility-driven style:

Francis, on the other hand, has used his Twitter account to name specific events on a handful of occasions, but to address one person, virtually never. He has tweeted about some of the many things he and Trump clash about, from immigration to climate change, but to put those as an attack on the president would be too self-aggrandizing, even for Trump.

For instance, when it comes to migration, the pope clashes with several Eastern European leaders, who are building walls in their nations (not only promising to do so), and even the United Kingdom, that left the European Union fueled by anti-migration feelings.

The pope will, however, remind Trump of his position on this issue, when he hands him a copy of his major environmental document, the encyclical Laudato Si’.

It’s a truth widely acknowledged that the two clash over virtually all major issues. The political messages they present are diametrically opposed and their versions of populism are markedly different.

Beyond migration and walls, they disagree when it comes to arms trading, something Pope Francis has spoken against over and over. The fact that Trump comes to Rome on the same tour he sealed a weapons deal worth $350 billion over 10 years with Saudi Arabia, may or may not come up on Wednesday. (Probably not).

On Easter Sunday, expressing a hope more than stating a fact, Francis urged the Risen Lord to “guide the steps of all those who work for justice and peace. May he grant the leaders of nations the courage they need to prevent the spread of conflicts and to put a halt to the arms trade.”

Yet despite the many things they could clash on, and their past exchanges, recently the two have shown interest in leaving the past in the past. After all, the two would get much more out a friendship of sorts than openly defying each other.

During the same Saudi Arabia stop where Trump signed his arms deal, he also showed the beginning of what could be a change in his rhetoric over Islam, calling this one of the world’s great religions, and urging leaders of all religions to work together. In style, his speech differed greatly to that of Francis’s, but there was an echo of the pope’s call during his recent trip to Egypt.

During his flight back to Rome from Fatima, Portugal, on May 13, Francis was asked about his expectations from a meeting with “a head of state who seems to think and act in a way contrary to your own?”

The pope answered by saying that he doesn’t make judgements about people without hearing them first.

True to himself, the pontiff also said he would begin by looking at the things over which the two can agree on: “There are always doors that are not closed … We have to find doors that are at least a little open in order to go in and speak about things we have in common and go forward. Step by step.”

The key, he added, is “respect for the other, saying what we think, but with respect, walking together. Someone sees things in a certain way: say so, be honest in what each of us thinks.”

He also said that he wasn’t planning on changing Trump: Proselytizing isn’t his style, he told reporters — in politics or religion.

Last but not least, Francis offered a glimpse of what he wants to talk about with the U.S. president: peace.

When Trump sits down with the spiritual leader of America’s 50-plus million Catholics, he’s going to be meeting the only person who, arguably, has a bigger megaphone than his own, one reason why he wants the meeting to go well.

If history and tradition hold, little will be known about what transpires in the papal library where the two will talk. Both the Vatican and the White House are bound to send out press releases, but at least the ones from the Church’s side are famous for being ambiguous and lacking much content.

One bet is safe. No matter the before, during and after, the meeting of these two modern titans is bound to be described as “cordial.”