WASHINGTON - Pope Francis stepped into some of America's most contested debates Wednesday, beginning his highly anticipated tour with a call for action on climate change and sympathy for immigrants.
Seizing an international spotlight, the 78-year-old pontiff drew tens of thousands of cheering supporters and onlookers, some of whom began gathering before dawn, and quickly made clear he had messages to deliver in his first visit to the United States.
Minutes after arriving at the White House, the pope appeared with President Obama in front of a crowd of about 11,000 on the South Lawn, and drew some of his loudest cheers by urging more care for what he called "our common home."
"Climate change is a problem which can no longer be left to a future generation," Francis said in slow, heavily accented English.
It was the first stop in an itinerary that carried him around the capital. At a meeting of U.S. bishops, Francis lauded their "commitment to bring healing" to victims of sex assaults by priests. And at a ceremony before thousands at the Basilica of the National Shrine of the Immaculate Conception, he presided over the first-ever canonization ceremony in the United States, elevating to sainthood Junipero Serra, a Franciscan missionary who helped spread the faith to California settlers in the 1700s.
The day also offered a possible glimpse of what may await the next cities on his trip - New York and Philadelphia, where an outdoor Mass celebrated by Francis on Sunday could attract as many as one million people.
Thousands crammed the National Mall and his motorcade route Wednesday, and his schedule nearly ground the District of Columbia to a halt. He will command the country's attention again Thursday, when he becomes the first pope to address Congress.
The pomp began Wednesday with a White House ceremony featuring a full-dress honor guard, a fife and drum corps in colonial garb, and a choir. Just the third pope to visit the White House, Francis stood with Obama under picturesque morning skies, with the flags of the U.S. and Vatican City stirring in a gentle breeze.
"Our backyard is not typically this crowded," the president quipped. But he called the gathering "a small reflection of the deep devotion of some 70 million American Catholics."
Obama then used Francis' visit to reinforce some of his top priorities.
The pope's message of mercy "means welcoming the stranger with empathy and a truly open heart - from the refugee who flees war-torn lands to the immigrant who leaves home in search of a better life," the president said, nodding to the immigration debates roiling the U.S. and Europe.
He hailed the pontiff's "humility" and focus on the poor and marginalized. "In these gentle but firm reminders of our obligations to God and to one another, you are shaking us out of complacency," Obama said.
And he thanked the pope for supporting America's renewed ties to Cuba and call "to preserve our precious world."
(He also pronounced the pope the first to share an encyclical on Twitter.)
In the second sentence of his address, the Argentine-born pontiff touched on immigration, saying that "as the son of an immigrant family" from Italy, he is happy to be a guest in a country "largely built by such families."
Among those watching from the lawn was a group of six proud Argentinians living in the U.S. They brought their homeland's flag to the White House, and beamed about the pope's emergence as a global leader.
"I'm amazed about the political impact," said Cristina Griffa. "He's being heard by the whole world."
On Thursday, Francis will speak to a bitterly divided Congress, one careening toward a potential government shutdown and gridlocked on most weighty issues.
At the same time, his emphasis on climate change, income inequality, and immigration has emboldened Democrats.
"For too many decades, the thought in the United States was that the Republican Party was the party of faith and the Democratic Party was the party of secularism, and neither of those is true," said Rep. Brendan Boyle, a first-term Philadelphia Democrat who is Catholic and attended the White House ceremony.
He said Francis' messages underscore that members of both parties can be motivated by religion.
Lawmakers and activists on an array of issues have sought to align themselves with the pope.
On Tuesday, Sen. Cory A. Booker (D., N.J.) cited the pope's concern for the less fortunate as he gave a speech advocating criminal justice reforms. A massive rally on climate change is planned on the National Mall on Thursday. And on Wednesday, White House spokesman Josh Earnest said that with an international climate conference approaching in Paris, he hoped the pope's "call to action would be heard around the world."
Social conservatives can still lay claim to the church's stands on issues such as abortion and same-sex marriage.
Antiabortion groups have rallied in Philadelphia ahead of the pope's trip, and House Republicans held a vote just before his arrival to eliminate federal funding for Planned Parenthood.
On his flight to Washington, the pope cautioned reporters who might label him a "lefty." And lawmakers and religious experts warned against trying to place the pope firmly on either side of the right-left divide in the U.S.
Democrats might like his message on the economy and environment, but will be less enthused by his conservative social stands, said Kevin Hughes, a Catholic historical theologian at Villanova University.
By the end of the pope's tour, Hughes said, "we should expect something that makes everybody a little uncomfortable."
Indeed, at the White House, Francis gave a nod to conservatives, saying an inclusive society must also respect Catholics' "deepest concerns and the right to religious liberty." He also said that while in Philadelphia following the World Meeting of Families, he plans to "celebrate and support the institutions of marriage and the family at this critical moment in the history of our civilization."
Most Republicans have eagerly anticipated his visit. Sen. Pat Toomey (R., Pa.), a Catholic, called Francis "a very inspiring figure."
The welcome event Wednesday included many of the features rolled out for any head of state, though the White House eschewed the typical 21-gun salute, a nod to the pope's humility and the dissonance of putting on a military display before a religious leader, said Earnest, Obama's spokesman.
After the ceremony, the two leaders met alone (along with the pontiff's interpreter) for about 40 minutes, the White House said, with Obama presenting gifts and relishing his chance to tell the pope about the building.
Even while taking on divisive issues, Francis' personal appeal gives him the ability to reach a broad audience, lawmakers and analysts said.
"One thing this pope has done, in ways I don't know that any other pope has done in my lifetime, is being able to speak to Catholics as well as non-Catholics," said Sen. Robert P. Casey (D., Pa.), who is Catholic.
Previous popes have expressed concern about poverty and inequality, said Hughes, the Villanova scholar. But Francis has drawn attention with his humble persona and "very different style," Hughes said. "That style has captured the imagination."
The evidence was apparent on the White House's back lawn Wednesday morning. Jeanette Manning was in line before 4 a.m. and waited more than five hours to see the pope - even though she is not Catholic.