Speaking to an Italian family association in 2018, Pope Francis compared the abortion of children with genetic problems to "what the Nazis did to purify the race. Today, we do the same thing but with white gloves."

A year later, Francis bluntly asked a journalist from Mexico if it's "fair to eliminate a human life in order to solve a problem? The answer to which is, 'No.' Second question: Is it fair to pay a sniper to solve a problem? No. Abortion is not a religious problem. … It is a problem of eliminating a human life. Period."

But the pope was careful in his Inauguration Day message to America's second Catholic president, assuring Joe Biden that he would "pray that your decisions will be guided by a concern for building a society marked by authentic justice and freedom, together with unfailing respect for the rights and dignity of every person, especially the poor, the vulnerable and those who have no voice."

The pope's text was examined closely after reports that the Vatican -- on behalf of progressive American bishops -- tried to stop the circulation of a sobering statement from the president of the U.S. Conference of Catholic Bishops. The letter from Archbishop Jose Gomez of Los Angeles addressed the challenge, and blessing, of working with "our first president in 60 years to profess the Catholic faith."

Clearly, Biden's piety had offered "solace in times of darkness and tragedy," said Gomez, leader of America's largest diocese and a crucial voice among Hispanic Catholics. He also praised Biden's "longstanding commitment to the Gospel's priority for the poor."

Nevertheless, Gomez noted that "our new President has pledged to pursue certain policies that would advance moral evils and threaten human life and dignity, most seriously in the areas of abortion, contraception, marriage, and gender. Of deep concern is the … the freedom of believers to live according to their consciences."

Cardinal Blasé Cupich of Chicago fired back on Twitter, attacking this "ill-considered statement on the day of President Biden's inauguration" while claiming "there is seemingly no precedent" for this action by Gomez.

The Pillar, a Catholic news website, reported that the Vatican Secretariat of State intervened to "spike" the statement from the U.S. bishops after objections from Cupich, Cardinal Joseph Tobin of Newark and some other bishops.

This clash was a rare example -- in public -- of ongoing tensions among American bishops about how to handle Catholic politicians who dissent, in word and deed, from centuries of church doctrines on life-and-death issues such as abortion and euthanasia, as well as hot-button topics such as sex, gender and marriage.

These tensions intensified in 2004, when a committee of American bishops sought Vatican advice on how to relate to Sen. John Kerry, a liberal Catholic who was the Democratic Party's presidential nominee. The question was whether his strong support for abortion rights should affect his ability to receive Holy Communion.

In a private reply, Cardinal Joseph Ratzinger -- now the retired Pope Benedict XVI -- said that if prominent supporters of abortion continue to present themselves for Holy Communion, against the advice of their local bishops, priests "must refuse to distribute it." 

The committee's leader -- the now-disgraced Theodore McCarrick -- claimed that Ratzinger's letter endorsed compromise. American bishops have been arguing ever since about what some call the "McCarrick doctrine." Meanwhile, Cardinal Wilton Gregory of Washington, D.C., has promised that he will not prevent Biden from receiving Holy Communion.

"Cardinal Cupich's tweets certainly intensified matters," said J.D. Flynn, editor of The Pillar, reached by telephone. "Bishops, ordinarily, just don't do things like that."

In his letter, Gomez stressed that Catholic leaders face the challenge of defending doctrines that do not "align neatly with the political categories of left or right or the platforms of our two major political parties." This affects issues ranging from race to economic justice, from health care to immigration.

Nevertheless, for America's Catholic bishops the "continued injustice of abortion remains the 'preeminent priority,' " argued Gomez. That said, the word "preeminent does not mean 'only.' We have deep concerns about many threats to human life and dignity in our society. But as Pope Francis teaches, we cannot stay silent when nearly a million unborn lives are being cast aside in our country year after year through abortion."