(CNN) — Pope Francis immediately dove into the whirlpool of U.S. politics on Wednesday, using his first direct address to the nation to weigh in on deeply divisive issues including climate change, Cuba, marriage and immigration.

The pontiff, speaking before 11,000 ticketed guests at an elaborate welcoming ceremony on South Lawn of the White House, signaled he will take on controversial issues during his six-day visit.

In remarks delivered slowly in accented English, Francis said he was ready to listen to the “hopes and dreams of the American people” and to offer guidance to those charged with shaping the nation’s political future “in fidelity to its founding principles.”

In comments that could antagonize Republicans, Francis endorsed President Barack Obama’s efforts on climate change and rebuilding ties with Cuba after more than half a century of estrangement.

He said it was “encouraging that you are proposing an initiative for reducing air pollution. Accepting the urgency, it seems clear to me also that climate change is a problem that can no longer be left to a future generation.”

“When it comes to the care of our ‘common home’ we are living at a critical moment of history,” he said.

Francis also made reference to one of the central themes of his papacy: that the modern global economy is enriching the few at the expense of the many.

“I would like all men and women of good will in this great nation to support the efforts of the international community to protect the vulnerable in our world and to stimulate integral and inclusive models of development,” Francis said.

But he also delivered a firm defense of traditional values, warning that the institution of marriage and family needed to be protected at “a critical moment in the history of our civilization,” remarks that could irk liberals months after the Supreme Court ruled in favor of same-sex marriage nationwide.

He said that it was right that society was “tolerant and inclusive” but warned that American Catholics were “concerned that efforts to build a just and wisely ordered society respect their deepest concerns and their right to religious liberty. That freedom remains one of America’s most precious possessions.”

Obama gently — but pointedly — argued that “here in the United States we cherish religious liberty.”

Stepping into another delicate political issue, the Argentine-born Francis pointedly noted that he was a “son of immigrants” — a sign that he could step into the debate later in his visit on how to handle millions of undocumented immigrants in the United States that has roiled the 2016 presidential campaign.

Obama and first lady Michelle Obama earlier greeted the Pope at the White House as he stepped out of his small black Fiat, which he is using to make a statement of humility in Washington, a city full of limos and hulking government SUVs.

On a glorious early-fall morning, the President and Pope stood together before an honor guard as a band played the national anthens for the Vatican and the U.S.

Obama paid warm tribute to the Pope as an individual as well as the leader of 70 million U.S. Catholics, saying he displayed “unique qualities” of a leader “whose moral authority comes not just through words but also through deeds.”

The White House has said that Obama will not seek to exploit the visit of Francis for political gain — but the president warmly welcomed the pontiff’s support on climate change and Cuba, for which he is trying to build domestic support.

“Holy Father, we are grateful for your invaluable support of our new beginning with the Cuban people, which holds out the promise of better relations between our countries, greater cooperation across our hemisphere, and a better life for the Cuban people,” Obama said.

The president also said the Pope had offered reminders that “we have have a sacred obligation to protect our planet.”

“We support your call to all world leaders to support the communities most vulnerable to a changing climate and to come together to preserve our precious world for future generations.”

The Pope’s visit is grinding Washington to a halt as thousands of people gather on downtown streets along a parade route Francis will trace in his popemobile following Oval Office talks with Obama.

The Secret Service, FBI and other law enforcement agencies are mounting a huge security operation, which is complicated by the Pope’s desire to interact directly with this crowds. Francis will later turn to pastoral duties, leading prayers at a Washington cathedral before celebrating an open air Mass in the evening.

Francis’ next political intervention could come on Thursday when he makes an address to a joint meeting of Congress. He will travel to New York and Philadelphia later in the week to wrap up his six-day visit.

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