“A person who thinks only about building walls, wherever they may be, and not building bridges, is not Christian,” Pope Francis said, in response to a reporter’s question about whether a Catholic could vote for Donald Trump. “This is not in the gospel,” he said on the flight back to Rome after his trip to Mexico, as reported by ABC News. He declined to say whether a Catholic could vote for Trump and said that even on the question of the border, “We must see if he said things in that way and in this I give the benefit of the doubt.” (The full transcript of the press conference can be found here.)

The pope was at the end of a five-day trip to Mexico, which had included a large Mass celebrated on Wednesday in the city of Ciudad Juarez, across the border from El Paso, Texas. Before the question was asked, the pope had been told that Trump has said that as president “he would deport 11 million illegal immigrants from the country, in that way separating families, and build a wall along the U.S. border with Mexico,” reported the Catholic magazine America.

The context, generally unreported, suggests the pope was reacting to the idea of building walls in a way that would unnecessarily break up families. Some Catholic observers noted that Francis spoke of someone who “thinks only about building walls” and said that the pope means that Trump was not speaking as a Christian, not questioning his status before God.

Trump reacted immediately, writing on his Facebook page that when ISIS attacks the Vatican, Francis will wish he had been president and eliminated ISIS. He blamed the Mexican government for using Francis, “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. … 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.” He also objected to the pope’s remark about his Christianity:

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.

The president of Liberty University, who has endorsed Trump for president, jumped in, comparing Francis to the religious leaders who persecuted Jesus. “Here’s the pope saying we have to choose the leaders — sounds like he’s saying this — that share his faith. Or share the Christian faith,” said Jerry Falwell, Jr. John F. Kennedy “would be rolling over in his grave right now” if he heard the pope. Francis’s comment “will hurt the pope more than it will hurt Donald Trump. I just don’t think people in this country take statements like that seriously.”

A Presbyterian who almost never attends church, Trump has said he doesn’t ask God for forgiveness and though he says the Bible is his favorite book, refuses to name a favorite verse when asked. In September he had described Francis as “a unifier. He wants to bring people together, and I think that’s a great thing. That’s what we have to do. We have to bring people together.”

Other Critics

The pope’s comments were not the first time a religious leader has questioned Trump’s understanding of Christianity. Russell Moore, the head of the Southern Baptist Convention’s Ethics and Religious Liberty Commission, said last year that “When one looks at the very serious moral character questions, from Trump’s involvement in the casino gambling industry all the way through to his attitude toward women, Donald Trump is the embodiment of everything that evangelical Christians have been standing against in American culture.”

When Trump spoke at Liberty College in January, Moore sent out several critical tweets, including one that said “This would be hilarious if it weren’t so counter to the mission of the gospel of Jesus Christ.” Responding to Falwell’s statement that “Donald’s Trump’s life has born fruit,” Moore tweeted “Absolutely unbelievable.”

Speaking to Fox Business News last Thursday, Trump had already attacked the pope as “a very political person.” He objected to Francis’s planned visit to the border. “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 they want to keep the border just the way it is. They’re making a fortune, and we’re losing.”

The comment was “very strange,” Vatican spokesman Fr. Federico Lombardi responded. “The pope always talks about migration problems all around the world, of the duties we have to solve these problems in a humane manner, of hosting those who come from other countries in search of a life of dignity and peace.”

Already battered this week by Ted Cruz as pro-choice (Trump claims to be pro-life now), Trump has now been identified by the pope as anti-immigrant. That combination, writes long-time Vatican observer John L. Allen on the website Crux, is “the Catholic Chernobyl.” While politically conservative Catholics may have already chosen a candidate and politically liberal Catholics won’t support Trump in any case, some of the Catholic vote will be in play in a general election in which

marginal shifts in one direction or another could have outsized consequences. If even a handful of Catholics in key states decide either to vote against Trump, or to sit things out, because of perceptions that he’s not reliable on important Catholic concerns, it could spell the difference between Trump negotiating a revival of The Apprentice or measuring curtains for the White House.

Although last August Trump had said of the Evangelical movement,”I love them. They love me. I love the evangelicals, and it’s really shown in the polls,” increasing numbers of influential Evangelicals besides Moore oppose him. “I do not see how we can [support Trump] if the Word of God is to be our guide and if it’s important to us that a candidate have a solid moral compass and a biblically based worldview,” wrote Michael Brown on The Stream. Several major state pro-family organizations have just published an Open Letter to Trump questioning his religious and conservative commitments in light of his record and his statements.