Here's why Donald Trump is feuding with Pope Francis

In a news conference on his plane held Wednesday, Pope Francis said, quite plainly, that he believed presidential candidate Donald Trump “is not Christian.” Francis specifically referenced Trump’s comments on immigration as his justification for the statement, according to the New York Times.

“A person who thinks only about building walls, wherever they may be, and not building bridges, is not Christian,” Francis told a reporter aboard the papal airliner, the Times reported.

Predictably, Trump issued a Trump-ian response, in which he said:

“For a religious leader to question a person’s faith is disgraceful. 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, with our current President. No leader, especially a religious leader, should have the right to question another man’s religion or faith. They are using the Pope as a pawn and they should be ashamed of themselves for doing so, especially when so many lives are involved and when illegal immigration is so rampant.”

Here’s Trump’s statement in full:

This isn’t the first time Trump has criticized Pope Francis. Earlier this year, when asked about the Pope’s impending visit to areas near the U.S.-Mexico border, Trump said:

“I think that the pope is a very political person. I think that he doesn’t understand the problems our country has. I don’t think he understands the danger of the open border that we have with Mexico.”

Trump also criticized Pope Francis’s predecessor, Pope Benedict, for resigning in 2013:

As Fusion reported on Thursday, Francis also commented on the treacherous conditions of the Mexican border on Wednesday.

“A crossing, a path filled with terrible injustices: enslaved, kidnapped, extorsioned, many of our brothers fall prey to the human trafficking business,” Pope Francis said. “We can’t deny this human crisis. No more death and exploitation!”

The feud between Trump and Pope Francis stems from their disagreements on the issue of immigration. Back in September of last year, the Pope spoke in front of a collection of bishops and declared, “Do not be afraid to welcome (immigrants)… I am certain that, as so often in the past, these people will enrich America and its church.” In a speech in Philadelphia a few days later, he commented once more on immigration, saying, “Many of you have immigrated to this country at great personal cost, but in the hope of building a new life. Do not be discouraged by whatever challenges and hardships you face.”

Trump, who has called for the immediate deportation of 11 million undocumented immigrants in the U.S., responded that the Pope’s comments were “beautiful,” but ultimately impractical.

“Well, I think his words are beautiful and I respect the Pope and I like the Pope very much,” Trump told CNN. “I will say this, we have a country that is going through tremendous problems.”

This isn’t the first time Trump has evoked ISIS when responding to Pope Francis’s views. In August of last year, when he was asked about the Pope’s views on capitalism. CNN’s Chris Cuomo asked Trump how he’d respond if the Pope expressed the idea that capitalism could be corrosive and harmful.

“I’d say ISIS wants to get you,” Trump told CNN. “You know that ISIS wants to go in and take over the Vatican? You have heard that. You know, that’s a dream of theirs, to go into Italy.”

Trump, who is a self-identified Presbyterian, does not appear to be an active churchgoer. When visiting a church in Iowa earlier this year, Trump placed money in the communion wafer tray by accident. And while picking up an endorsement from Liberty University president Jerry Falwell Jr., Trump provoked snickers from some religious types by referring to the second book of Corinthians as “Two Corinthians.”

Pope Francis probably would not have endorsed Trump, even before this week’s feud. But the Pope isn’t likely to campaign against him, either. In his most recent interview, Pope Francis has said he was “not going to get involved in that” when asked if he might attempt to sway Catholic voters in the American presidential election.

Despite Republican voters seeing Trump as by far the least religious presidential candidate, 52% of white evangelicals still think he would do a “great or good job,” according to a Pew Research Poll from late January, sharing the highest marks of confidence with Ben Carson.