Pope Francis is not afraid of a billionaire real estate mogul who is running for president of the United States, especially when the candidate takes aim at him and the vulnerable.

On the papal plane on Thursday, Pope Francis said that Donald Trump, who has taken a hard line on immigration, “is not a Christian” for vowing to have mass deportations if he becomes president and saying that he will force Mexico to build a wall along the southern border, the New York Times reported.

“A person who thinks only about building walls, wherever they may be, and not building bridges, is not Christian,” said the pope, a vocal advocate for immigrants and the vulnerable, after a reporter on the plane asked him about Trump.

At a campaign rally after the pope’s comments, Trump quickly fired back. "No leader, especially a religious leader, should have the right to question another man’s religion or faith," he said.

The entanglement between the GOP presidential candidate and the pontiff began last week when Trump criticized the pope’s visit to Mexico, where Francis arrived Friday night.

“I think that the pope is a very political person,” Trump said in a media interview.

“I don’t think he understands the danger of the open border that we have with Mexico,” Trump said to Fox Business Network. “I think Mexico got him to do it because they want to keep the border just the way it is. They’re making a fortune, and we’re losing.”

In Mexico, Francis made it a point to visit the border area and address immigration.

He conducted a Mass in the city of Cuidad Juárez, across the Rio Grande from El Paso, and lay flowers at a site commemorating those who have died crossing the border. During the Mass, attended by more than 200,000, he urged compassion for immigrants who take risks to find for a better life.

“I say only that this man is not Christian if he has said things like that,” Francis said about Trump, stressing that he is not seeking to influence the presidential election. “We must see if he said things in that way, and in this I give the benefit of the doubt.”

“Thank God he said I was a politician because Aristotle defined the human person as ‘animal politicus,’” he said. “So at least I am a human. As to whether I am a pawn, well, maybe. I don’t know. I’ll leave that up to your judgment and that of the people.”

The pope also suggested on the flight back to Rome from Ciudad Juárez that women facing the possibility of contracting the Zika virus could be allowed to use contraception. “Avoiding pregnancy is not an absolute evil,” Francis said, and in some circumstances it could be allowed as “the lesser evil.”

The pontiff stressed that abortion is an entirely different matter. “It is killing one person to save another. It is what the Mafia does," Francis said. "It is an absolute evil.”

At the campaign rally Thursday morning, Trump said, “The Mexican government and its leadership has made many disparaging remarks about me to the pope because they want to continue to rip off the United States, both on trade and at the border, and they understand I am totally wise to them.”

“The pope only heard one side of the story – he didn’t see the crime, the drug trafficking and the negative economic impact the current policies have on the United States. He doesn’t see how Mexican leadership is outsmarting President Obama and our leadership in every aspect of negotiation.”

“For a religious leader to question a person’s faith is disgraceful," he added. "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.”

Fox News producer Christopher Snyder contributed to this article.

Like us on Facebook
Follow us on Twitter & Instagram