The rock-star papal journey -- pioneered by the charismatic Pope John Paul II, but tamed by the charismatically challenged Pope Benedict XVI -- is back. In his visit to Cuba and the United States, Pope Francis is certain to draw huge crowds and make plenty of news.

But his speeches to Congress and the United Nations won't answer this central question: How successful will he be at the mountainous task of reforming the papacy and the Roman Curia, the powerful administrative core of the Vatican? In his book "Can We Save the Catholic Church?," the eminent Swiss theologian Hans Küng put it this way: "Pope Francis: a paradox? Is it possible that a Pope and a Francis -- obviously opposites -- can ever be reconciled?"

At the 2013 conclave to choose a new pope when Benedict resigned, the College of Cardinals elected Jorge Mario Bergoglio of Argentina. Minutes later, he became the first pope to take the name Francis. His model was Francis of Assisi, who abandoned warfare and wealth, embraced poverty and celebrated all creation. Sound familiar? Pope Francis has made outreach to the poor and care for our common home key themes of his papacy.

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The poor man of Assisi and the pope share something else: the "Roman system," Küng's term for the absolutist, monarchic power that the Vatican exerts. Pope Francis must overcome the Curia's obduracy to bring about real change.

St. Francis went to Rome in 1210 for permission from the Curia and Pope Innocent III to establish his new religious order. Not long after the saint's death, Küng argues, the order was under the sway of papal politics. "If, then, it was possible that Francis of Assisi and his followers were finally domesticated by the Roman System," Küng writes, "then obviously it cannot be out of the question that Pope Francis could also be trapped in the Roman System which he is supposed to be reforming."

The Curia moves slowly, resisting change. Its leaders can tolerate the pope's decision to live in a Vatican guesthouse, instead of the luxurious papal apartments. They can do little more than roll their eyes at his breaks with tradition, such as washing the feet of a Muslim woman on Holy Thursday. But they'll fiercely resist any real realignment of the stubbornly self-protective Curia itself and a decentralization that shares church leadership more fully with bishops.

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Still, Francis has made a start. He has begun fixing Vatican finances, and he has named a nine-member Council of Cardinals to help him navigate reform, but he hasn't met with the panel often. Some feel reform is moving too slowly -- others, too fast. Bishops have grumbled in private and in public -- about Francis' critique of capitalism, for example, and his decision to issue an encyclical in June on climate change, a subject in which critics say he has no expertise.

One commentator, Maureen Mullarkey, wrote in First Things, the conservative journal of religion, that Francis is "an ideologue and a meddlesome egoist." Gee, what got her all wound up? It was the pope's declaration: "If we destroy creation, creation will destroy us."

Even before his encyclical, critics pre-emptively griped. Outside the narrow circle of bishops and theologians who study them, papal letters tend to arrive to a vast chorus of yawns. But this one got unprecedented attention in advance -- evidence of this pope's power to communicate.

In his 2013 apostolic exhortation, "Evangelii Gaudium," or "The Joy of the Gospel," Francis set out his vision for spreading the Gospel and changing the church. In effect, he has begun a salutary downsizing of the papacy. That's not as revolutionary as it sounds. Even John Paul II, the, autocratic über-pope, called for proposals to rethink the way papal primacy works.

"We have made little progress in this regard," Francis wrote. "The papacy and the central structures of the universal Church also need to hear the call to pastoral conversion."

Francis wants the clergy to be "shepherds with the smell of sheep." He enforced that standard dramatically by removing a German bishop who spent $43 million on his residence. Francis also showed his emphasis on finding the right shepherds by personally choosing Archbishop Blase Cupich to lead the Archdiocese of Chicago. But he also demonstrated that bishop selection is tricky. In Chile, he appointed a bishop so sharply criticized for defending a sexual abuser priest that protesters disrupted the bishop's installation Mass.

Beyond reforming the Curia and bishop selection, Francis has to reshape the College of Cardinals so it does not elect a successor who'll erase whatever gains he's made. He has already named cardinals from countries that had never had one, but Italy is still vastly overrepresented, and Francis has much more work to do to protect his reforms from a future counter-reform pope.

As to changing church teaching on key issues, that's not happening. We've heard a softer tone, such as the pope's decision to make more widespread the practice of allowing women who have procured abortions to get absolution from any priest, not just from a bishop. At the October synod on the family, in Rome, we'll see whether he can change church teaching, for example, to allow divorced Catholics to receive communion. For a possible clue, look to his homily at the Mass concluding the Vatican-sponsored World Meeting of Families in Philadelphia.

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So, for now, enjoy the spectacle. But Küng's pivotal question -- whether the simplicity of Francis, the saint and the pope, or the smothering power of the "Roman system" will prevail -- will not be answered on this trip.

Bob Keeler is a former member of Newsday's editorial board.