ROME — “They call me a heretic.”

Not the words you’d expect to hear from the head of the Roman Catholic Church. But that’s what Pope Francis told a group of fellow Jesuits in Chile earlier this year, acknowledging the fierce pushback from arch-conservatives in the Vatican.

Celebrated by progressives around the world for his push to update and liberalize aspects of church doctrine, Francis is facing fierce blowback from traditionalists who take issue with his openness to Muslim migrants, his concern for the environment and his softer tone on divorce, cohabitation and homosexuality. Opposition has become so heated that some advisers are warning him to tread carefully to avoid a “schism” in the church.

Father Thomas Weinandy, a former chief of staff for the U.S. bishops’ committee on doctrine, has accused Francis of causing “theological anarchy.” Another group of bishops has warned Francis risks spreading “a plague of divorce.” Last fall, more than 200 scholars and priests signed a letter accusing Francis of spreading heresy. “This was not something I did lightly,” Father John Rice, a parish priest in Shaftesbury in the U.K. said, claiming the pope’s liberal push has caused “much division and disagreement, and sadness and confusion in the church.”

“It’s not merciful to let people continue to sin and say nothing,” Rice said. “If you see a child trying to put his hand in a fire you say stop.”

Deviating from doctrine is bad enough. But Francis is also under fire from the Vatican’s civil service, known as the Roman Curia.

On becoming Pope, Francis set a new tone by setting up his headquarters in a humble guesthouse for priests rather than the grand apostolic palace — a gesture of humility that carried with it an implied criticism of past excesses. He also did away with the system of automatically giving a cardinal’s hat to bishops in certain posts. Conservatives have been irked by some of his more liberal stances. In 2015, Francis ordered every parish to host two refugee families. And last week, in his most explicit acceptance of homosexuality yet, he told a gay Catholic that God had made him that way and that his sexuality “does not matter.”

The focus of most traditionalist dissent has been Francis’ Amoris Laetitia, an “apostolic exhortation” — a type of papal communication — in which he called for a “merciful” approach to divorcees and opened the door for those living with new partners to take communion with their priest’s permission.

By rendering doctrine more ambiguous, Francis is effectively undermining the church’s authority and reducing the role of priests to that of companion and advisers to their parishioners — a thorny issue that dates back to the Vatican II reforms of the 1960s, according to one diplomat. “The battle is between [loyalty to retired Pope] Benedict, vestments, liturgy and rules, and Pope Francis, who wants priests to use their own judgment and humanity in their reading of individual situations,” the diplomat said.

The shift may seem like small beer to non-Catholics — and Francis’ suggestions are already the practice among many priests. But the changes have become the touch-paper for conservative dissent, enflaming mutterings of disapproval into open mutiny. The Vatican’s conservative flank is increasingly taking action.

The rebellion has grown to include not just arch-conservatives but also more middle-of-the-road Catholics who adhere to the church’s teachings on abortion and marriage and resent Francis’ flexible approach.

At a conference on “the limits of papal authority” in Rome last month, Cardinal Raymond Burke, one of the key figures leading the charge against Francis, reminded the audience the pope’s power is not “magical.” If a pope has “deviated from the faith” he “must as a duty, be disobeyed,” said Burke.

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Deviating from doctrine is bad enough. But Francis is also under fire from the Vatican’s civil service, known as the Roman Curia. With John Paul II ill for the last 10 years of his life and Benedict XVI little inclined to engage in matters of the mundane, the Curia was used to running itself, said David Willey, author of “The Promise of Francis.” For close to 20 years, the Vatican was “rudderless.”

The Curia Francis inherited was riddled with financial irregularities, and inclined to lobbies and leaks. Cardinal Bertone, the pope’s No. 2 when he took over in 2013, called it “a nest of vipers and crows” after he was sacked. “There are factions, pockets of opposition,” said Willey. “It’s a very cliquey organization.”

In trying to make the Curia more service-minded, Francis has also repeatedly berated its members for their careerism and ambition. “He has been very tough on the Curia — too tough really,” according to a former Vatican consultant. “Most are very educated, trying to do the right thing, and they have been disappointed by that.”

“Like any huge bureaucracy, the Vatican is set in its ways,” said Lord Patten of Barnes, a former chairman of the BBC who led a committee commissioned by the pope to identify potential reforms in the Curia’s communications departments.

He was warned of the sensitivity of the job when he took it on, he said: “I was told ‘It’s like peeling an onion, you have to go a skin at a time.’ But in my opinion if you peel an onion like that you end up crying.” Although he initially expressed frustration at the lack of progress, Patten now says Francis cannot be expected to run the Vatican “like the chief executive of McKinsey’s.”

To others, Francis has not been firm enough in his resolve to reform the Curia. Campaigner Marie Collins, who was recruited to advise the Vatican in tackling its clerical abuse scandal, resigned earlier this year, citing a lack of decisive action by Francis and the strength of resistance to some reforms. “We were told, ‘This is our business, we’ve been doing it for years,’” she said.

The Curia, Collins said, resented the fact that her committee was independent and reported to Francis directly: “They did not want outsiders, with lay people and women, judging them. There is a culture of clericalism: Lay people are not respected.”

Meanwhile, many liberals in the church are frustrated because change hasn’t gone far or fast enough. Francis promised to put women in positions of power, but his appointments so far — such as his nomination of a woman as director of the Vatican Museums — have been timid. Neither were progressives impressed by the Vatican’s decision to block the former Irish President Mary McAleese from speaking at a conference on women last month. The decision, they said, reflected poorly on Francis.

When the conference was eventually moved outside the Vatican, McAleese was vocal about her displeasure about the arrangement, calling the Vatican “a male bastion of patronizing platitudes to which Pope Francis has added his own quota.” The Church, she said, is limited to “recycled thinking among a hermetically sealed, cozy, male clerical elite.”

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Francis appears to be under siege. But many describe him as a canny political operator, and doubt he’ll buckle under the pressure. “I don’t think a political innocent could be a senior Jesuit, run a huge diocese in Argentina and be pope,” Patten said.

Francis is a “master strategist” who achieves his agenda “by stealth and cunning,” according to the diplomatic observer. He prefers shuffling people around rather than directly confronting or sacking them. But he has on occasion shown that he doesn’t shy away from direct conflict and has successfully faced down challenges to his authority, instigated by Burke, from the Order of Malta. “He doesn’t back down, he is really tough and steely,” the observer said.

Last week, after meeting and apologizing to victims of sexual abuse by priests in Chile, Francis summoned the county’s entire conference to Rome, rebuking them so severely that they resigned en masse. Close allies claim Francis is not worried about public disagreement. “He tries to draw [dissenters] into the open. He thinks that’s healthy,” a person close to the pope said. “But some of it is coming from a very bitter place.”

Some, such as long-term Vatican watcher Massimo Franco, claim that the “crows” that crippled Benedict and shaped the poisonous end of his reign have returned — and are behind a string of recent attacks on Francis’ allies. Figures close to the pope have been linked to a series of scandals, which, some claim, are intended to discredit Francis and make his regime look as chaotic and dysfunctional as his predecessor’s.

The most frequent targets are those charged with tackling the Vatican’s murky finances. A vice director was sacked in November for “administrative violations,” and a month later, a letter in which the bank’s director appeared to confess to wrongdoing was sent to clerics and staff. (He denied writing the letter and rejected its contents.)

The outspoken and bullish Cardinal George Pell — who had taken it upon himself to clean up the church’s finances — is also currently facing trial in Australia over allegations of sexual abuse. Cardinal Oscar Maradiaga, the coordinator of a powerful group of cardinals who advise Francis on reform, was accused of drawing €35,000 euros a month from the Catholic University of Tegucigalpa, Honduras — a major blow to the pope’s vision of a church for the poor.

Not everybody — even on Francis’ side — is convinced that the charges are entirely without warrant. “Talk of a plot is overblown,” said one senior member of the Curia. “We need to ask, did these accusations have substance, rather than assume they are a conspiracy.”

If Francis can hold on for several more years until he can rally enough cardinals, he may be able to guarantee that his legacy is not lost.

Despite Francis’ unflagging demeanor, there are signs that the personal attacks may be wearing him down. He has said that he avoids engaging with online haters for his own “mental health.”

The fight, and the threat of a schism, won’t end with his death or retirement. For some faithful, he represents longed-for change and reform. “There is so much enthusiasm from the grassroots,” said a close ally. “Anyone trying to wind the clock back would find themselves alone in the church.”

But if Francis fails to ensure a liberal succession before he’s gone, his conservative opposition could yet prevail.

A pope’s real power lies in his mandate to appoint the cardinals who will vote in his successor, and there too Francis has been making strides. In June, he will hand out 14 new red hats, including three to key collaborators. At that point he will have selected 47 percent of the 125 voter-cardinals eligible to choose his successor, just shy of a majority.

If Francis can hold on for several more years until he can rally enough cardinals, he may be able to guarantee that his legacy is not lost. “It’s a numbers game,” said Willey.

Hannah Roberts is a British freelance foreign correspondent and producer based in Rome.