Archbishop Charles J. Chaput was by all accounts the consummate host for Pope Francis during the Holy Father's weekend in Philadelphia last month, smiling from the back of the popemobile as it wound around the Benjamin Franklin Parkway in a historic visit meticulously planned over more than a year.

And since Chaput came to Philadelphia from the Rockies four years ago, he has taken anything but a backseat - speaking out in defense of traditional church teachings to become one of the most formidable prelates in the Roman Catholic Church.

So naturally, almost as soon as the American Airlines jet lifted off to return Pope Francis to Rome, speculation started over whether Chaput, 71, might be in line for cardinal - a post now held by only nine men in the nation.

His dues are well-paid: The former archbishop of Denver and bishop in Rapid City, S.D., Chaput took the helm here as the Philadelphia Archdiocese grappled with the aftermath of two grand jury reports on clergy sexual abuse, as well as declining membership and financial woes.

Still, despite what experts agree is his notable religious career, the four-cornered, red silk hat could be a long shot for Chaput. They say it's less a reflection on him than on the current direction of the church worldwide, and the priorities of its leader.

"Under normal circumstances, it would be safe to say he would be receiving one," said Austen Ivereigh, a London-based Roman Catholic journalist and Francis biographer. "But Francis has changed the rules of the game."

The pontiff has shaken up the way cardinals are selected, no longer basing the call primarily on one's career or the historical significance of one's pulpit, but more on places overlooked or in crisis.

Philadelphia's archdiocese, for all its history, is small compared with the swelling parishes of the U.S. South and West.

Limits on the College of Cardinals' size may work against Chaput as well. As the Rev. Thomas Reese, an analyst for the National Catholic Reporter, put it, "There are only so many red hats to go around."

At age 80, cardinals lose their most important power: a vote in the conclave that picks a pope. Only 120 cardinals can have that power. The current total is 118 - including just nine U.S. cardinals.

Any appointments will likely wait until more vacancies open. Experts agree it's impossible to predict whether Chaput will be elevated, but the trajectory of the church and Pope Francis' style offer some clues to those who study him closely.

Philadelphia had cardinals for nearly a century - from Dennis Dougherty to John O'Hara, John Krol, Anthony Bevilacqua, and Justin Rigali, before Chaput took over as archbishop in 2011.

But the earlier cardinals oversaw a growing flock. In the 19th and early 20th centuries, the archdiocese produced missionaries by the hundreds and seminary classes as big as 700. (The latest class at St. Charles Borromeo Seminary in Wynnewood was 20 men - up from recent years.) Part of an East Coast bastion of Catholicism stretching from Boston to Baltimore, Philadelphia's pews were once packed with Irish, Italian, German, and Polish immigrants.

"It was a well-oiled machine, known as the daughter of the Vatican and an international model of vibrance and fidelity," said Rocco Palmo, Philadelphia-based writer of the Vatican insider blog Whispers in the Loggia.

In recent years, however, the Catholic demographic has shifted and flocks have dwindled, hastening the merging or closing of schools and parishes.

Philadelphia has lately wavered between sixth- and seventh-largest U.S. diocese, with some 1.4 million members in the five counties that make up the archdiocese.

Compare that with Houston, where in 2007 Daniel DiNardo became the first cardinal in the South amid rapid growth there. Fueled by an influx of Latino immigrants, the diocese of 1.3 million Catholics has opened three new schools and 27 churches - several seating 1,500 people or more - since 2006.

Or Los Angeles, where Archbishop Jose Gomez has said more Catholic babies (70,000) were baptized last year than in New York, Chicago, Philadelphia, and Washington combined. With only a few U.S. cardinal hats to go around, Gomez, a Mexican immigrant, is seen as a likely choice. He would also be the nation's first Hispanic cardinal.

Francis also may want to see more of an international balance in the college. As an Argentine, he is from a continent where countries such as Brazil have fewer cardinals - but more Catholics - than the United States.

"We may think we're the center of the whole, but in the Catholic Church, we aren't," Reese said.

He noted that Francis hasn't named a cardinal for Venice, either - but did give a biretta to the archbishop of Lampedusa, who is credited with welcoming hundreds of thousands of African and Middle Eastern refugees to that tiny Mediterranean isle.

That Lampedusa has a cardinal and Philadelphia doesn't is no accident, Francis' biographer said.

"It's a deliberate attempt to reshape the college to allow the voices of the margins," Ivereigh said.

The red hat is no longer a marker of achievement - "He doesn't believe in an ecclesiastic career ladder."

Who would want a cardinal's life? While lodging and amenities, like those of priests and bishops, are taken care of, some reports put cardinals' salaries as low as $26,000.

But the position is attractive. For the few U.S. cardinals, the title comes with a built-in megaphone on any number of issues. Cardinals also craft church policy worldwide - as well as elect the next pope.

"Every seminarian wants to be a cardinal," Reese said. "It's one of the temptations of the clergy - the kind of ambition Pope Francis complains about, but that's just part of reality."

Geography and population aside, the pope will pick people he trusts to choose his successor, Reese said. "The question is, is Chaput that kind of man for him?"

Some have wondered whether the two men are too different - Francis has shied away from some divisive topics while championing the poor and the overlooked. His comment "Who am I to judge," spliced from a conversation about a homosexual man, was broadcast worldwide as evidence of his inclusive message.

Chaput, a leading conservative, has tackled topics such as same-sex marriage and abortion head-on, in 2012 branding President Obama's call for religious-affiliated hospitals and charities to offer employees free contraception coverage "the embodiment of a culture war," and saying last year that Holy Communion for divorced and remarried Catholics "can't be a reality in our lives."

But if their tones differ, the two are fully in line theologically, Ivereigh said: "If Chaput does not receive a red hat, it indicates neither displeasure nor difference between Francis and Chaput."

Last year, Francis named Chaput to the Vatican's Pontifical Council for the laity. He was also selected to participate in the Synod on the Family, an annual gathering of church leaders now taking place in Rome.

Robert George, a law professor at Princeton University and longtime friend of Chaput's, dismissed notions that the two are so different. "The pope is not a theological liberal," said George, who is Catholic. "He upholds the church's moral teachings very strongly. You have to take the edge of myth off both men. When you do that, you see they're quite similar."

Chaput, a Potawatomi and the first Native American archbishop, was ordained in the Capuchin order of Franciscan friars (from whom Francis took his name). In keeping with that order's tradition, George said, Chaput is no "high liver." In 2012, he sold the 16-room mansion that had housed his Philadelphia predecessors because he found it excessive. Like the pope, he carries his own bags.

Spokesman Ken Gavin said neither the archdiocese nor Chaput, now attending the Synod in Rome, would speculate on whether he might become a cardinal.

George said Chaput would never discuss the title, which would, among other duties, mean splitting his time between Philadelphia and Rome. Such speculation, George said, would fly in the face of his friend's religious vows.

"He is the kind of man who not only would never talk about it even to an intimate friend," George said, "but would discipline himself not to even think about it, for fear he would fall into the vice of ambition."