Pope Francis said Republican presidential candidate Donald Trump is "not Christian" because of his views on immigration Feb. 18. Pope Francis was speaking to reporters on his way back to Rome from Mexico. (Reuters)

Republican presidential candidate Donald Trump fired back today at Pope Francis for suggesting that anyone who wants to build a border wall "is not Christian."

Trump said it is "disgraceful" for a religious leader to question a person's faith. Trump had kicked off the back-and-forth before the pope set off for Mexico by calling Francis  “a very political person."

Here's how the exchanges played out:

DONALD TRUMP: On Fox Business Network last week, Trump said: 

"I don't think he understands the danger of the open border we have with Mexico. And 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 Vatican responded by arguing that the pontiff wasn't jumping into the U.S. presidential race but that his concern for migrants is a global issue.

VATICAN: Responding late Tuesday, the Rev. Federico Lombardi said:

"The pope always talks about migration problems all around the world," the Associated Press reported.

Lombardi added that Pope Francis also focuses on "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."

POPE FRANCIS: After finishing his trip to the Mexican border, Francis told journalists: 

“A person who thinks only about building walls — wherever they may be — and not building bridges, is not Christian. This is not in the Gospel."

"As far as what you said about whether I would advise to vote or not to vote, I am not going to get involved in that. I say only that this man is not Christian if he said things like that. We must see if he said things in that way and in this I give the benefit of the doubt."

DONALD TRUMP: Responding to the pope's comments, Trump released a statement saying: 

“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.”

Trump has said that he will force Mexico to build a wall to keep illegal immigrants from traveling to the United States.

Immigration and migrants are hot-topic issues in the Republican presidential race. Both Trump and his Republican rival, Sen. Ted Cruz, have promised to deport all of the millions of undocumented immigrants in the United States. Trump has vowed to block Muslims from entering the country, build a wall across the border with Mexico, revoke birthright citizenship and other measures.

Pope Francis arrived in Ciudad Juarez, a Mexican border town across from El Paso, Tex., on Wednesday. It was the last stop on his six-day tour of Mexico, where he highlighted corruption, violence and drug-trafficking. His stop in Juarez included a call for compassion for the thousands of migrants crossing the border into the United States.

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