Donald Trump said it was "disgraceful" on Thursday for Pope Francis to question his faith, igniting a religious war of words between the Republican presidential front-runner and the Holy Father just two days before the primary in heavily-Christian South Carolina.
The pope told reporters that someone like Trump "who thinks only about building walls-wherever they may be-and not building bridges, is not Christian," according to the Associated Press. He made the remarks after leaving Mexico en route back to Vatican City.
The pope said he'd "give the benefit of the doubt" since he hasn't heard Trump's plan himself, according to AP, adding, "I say only that this man is not Christian if he has said things like that."
Trump has proposed bolstering American border security by building a wall along the U.S.-Mexico border and having Mexico pay for it in an effort to combat illegal immigration.
"For a religious leader to question a person's faith is disgraceful," Trump said in a statement. "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."
Trump said Mexico is using the pope like a "pawn."
"If and when the Vatican is attacked by ISIS, which as everyone knows is ISIS's ultimate trophy, I can promise you that the Pope would have only wished and prayed that Donald Trump would have been President because this would not have happened," Trump said.
The pope has become an increasingly political figure in recent months. Last fall, he visited the United States and spoke to a joint session of Congress. His rhetoric at times seemingly transcended traditional political party divisions: progressives have praised his criticism of income inequality and his calls to combat climate change, while social conservatives have praised his stances against abortion and same-sex marriage.
Already, presidential candidates are being asked to weigh in on the pope's comments, even before they've had a chance to hear them for themselves.
Speaking to reporters Thursday before an event in Anderson, South Carolina, Sen. Marco Rubio said he hadn't seen Pope Francis' full comments, though he added, "we're also a sovereign nation and we have a right to control who comes" into the United States "and how they come in."
A Bloomberg Politics poll conducted Feb. 13-16 found 41 percent of likely Republican primary voters in South Carolina say Trump has the right approach to illegal immigration; rival Sen. Ted Cruz was a distant second at 16 percent.
That same poll had Trump trouncing his competitors in the overall horse race: Trump garnered 36 percent, followed by Cruz at 17 percent.
The poll also found 35 percent said Trump wasn't religious enough to be a good president. Cruz led with 24 percent on the question of which candidate shares the religious values of the people of South Carolina.
Trump, a Presbyterian, has recently courted the evangelical vote in South Carolina after doing so in Iowa, where he placed second behind Cruz in the Feb. 1 caucuses. He has received prominent endorsements within the evangelical community, including Jerry Falwell Jr., son of the late Reverend Jerry Falwell, a dominant force behind creating the conservative "Moral Majority" in the 1980s.
Catholics are seen as an important swing vote in presidential elections. A majority of voting Catholics supported President Barack Obama in 2008 and 2012. They backed former President George W. Bush for re-election by a narrow margin in 2004, but went for Democratic nominee Al Gore in 2000, according to Pew Research Center.