A former Vatican leader who was excommunicated earlier this year has urged Catholics to back former President Trump, arguing that Vice President Harris will build the "most ferocious dictatorship" if elected.

Former Roman Catholic Archbishop Carlo Maria Vigano, who previously served as the Vatican’s ambassador to the U.S., wrote in an open letter Tuesday to American Catholics that Trump is "the only possible choice" as "voting for Kamala Harris is morally inadmissible and constitutes a very grave sin."

"In this election you must choose between two radically opposed ways of conceiving the government of your Nation: you are called to choose between democracy and dictatorship, between freedom and slavery," Vigano wrote.

Vigano wrote that while Trump has "serious problems in his positions" on abortion and assisted procreation, the former president aims to protect the "fundamental freedoms of citizens."

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Carlo Maria Vigano

Archbishop Carlo Maria Vigano was excommunicated from the Catholic Church in July after being found guilty of schism. (Reuters/Gregory A. Shemitz, File)

"In Donald Trump’s America, every Catholic can practice their Faith and educate their children in it without interference from the State," the former archbishop wrote.

Vigano called Harris "an infernal monster who obeys Satan," arguing that in her America, Catholics and Protestants "are considered fundamentalists to be marginalized and eliminated, and their children are considered the property of the State."

Carlo Maria Vigano

Vigano served as the Vatican's ambassador to the United States, also known as the Apostolic Nuncio, from 2011 to 2016. (Reuters/Gregory A. Shemitz, File)

"Trump’s America can become great and prosperous again," he wrote. "Harris’ America is destined for invasion and for moral, social, and economic destruction: the most ferocious dictatorship."

Under the Biden-Harris administration, Vigano described American cities as having become "dumps filled with derelicts and criminals, drug dealers and addicts, prostitutes and robbers," while schools have turned into "dens of indoctrination and corruption" starting in kindergarten.

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Vigano also accused Harris as being a "puppet" of former President Obama, former Secretary of State Hillary Clinton and liberal megadonor George Soros.

Trump, Vigano argues, is "committed to freeing America" from what he called the "tentacled grip" of the so-called "deep state."

Carlo Maria Vigano

Vigano penned an open letter last week urging Catholics in America to back former President Trump over Vice President Harris. (Reuters/Gregory A. Shemitz, File)

Vigano served as the Vatican's ambassador to the United States, also known as the Apostolic Nuncio, from 2011 to 2016.

In July, Vigano was found guilty of schism and excommunicated from the Catholic Church after years of intense disagreements with Pope Francis. Schism is the act of withdrawing submission to the pope or from the communion of Catholics who are subject to him.

Catholics historically voted for Democrats until the 1960s and early 1970s, when crime and cultural issues came to the fore alongside economic concerns.

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Today, Catholic voters are evenly split between the two parties, and whichever side captures the majority is usually the side that wins the White House.

Fox News Digital’s Chris Pandolfo contributed to this report.