President Obama’s talk with President Raúl Castro of Cuba drew praise from Latin American leaders and an editorial in El Universal with the headline “A New Era in the Americas.” Credit Stephen Crowley/The New York Times

And the new star in Latin America is … the United States?

The reviews are in, and while the United States still faces plenty of tricky relations in a diverse region of 35 states, President Obama walked away with more salutes than swipes from a regional Summit of the Americas where the United States usually takes a drubbing.

The question now is whether Mr. Obama and his successors can capitalize on the new credibility Washington has earned, primarily through his reconciliation with Havana.

Mr. Obama sat down for an hourlong meeting with President Raúl Castro of Cuba, which the United States allowed to attend the summit for the first time since the meetings began in 1994. It was the first meeting between leaders of the Cold War-era foes.

Mr. Obama also announced that Brazil’s president, Dilma Rousseff, will be accorded a state visit to Washington in June, after she canceled one in 2013 over American tapping of her communications.

He even briefly chatted with President Nicolás Maduro of Venezuela, who just a few hours earlier had railed against American “imperialist interference” and threatened — but notably failed to deliver to Mr. Obama — a petition demanding that the United States lift sanctions against several Venezuelan officials accused of human rights violations.

“The world of politics and diplomacy is, in good measure, one of grand symbols,” the Mexican newspaper El Universal heralded Sunday in an editorial headlined “A New Era in the Americas.”

It was not all sweetness and light, however.

Mr. Castro roasted the United States, at considerable length, over what he called its history of oppressing Cuba. The presidents of Venezuela, Bolivia and Argentina followed suit.

Mr. Obama deflated expectations that he would announce Cuba was being removed from the American government’s list of nations that sponsor terror — a designation that many regional leaders find baffling, and that prevents nations from reopening their embassies. But for a region long tired of the mutual animosity and perplexed at the Cold War-era embargo, it seemed progress enough that the presidents were talking without hostility.

Perhaps more important was the shift of tone at this year’s meeting. The maligning from the left that had tended to dominate previous summits took a back seat as Mr. Castro called an American president “honest” and humble and even apologized for getting carried away with revolutionary rhetoric.

Now, the question is how will the United States spend the considerable political capital it has accrued in the region to address vexing issues such as corruption, impunity and the fragility of democracy or, in the case of Cuba, its glaring absence?

Mr. Obama acknowledged this at his news conference before leaving the summit Saturday, saying the United States was not giving up on democratic hopes for Cuba, just the approach.

“We have very different views of how society should be organized and I was very direct with him that we are not going to stop talking about issues like democracy and human rights and freedom of assembly and freedom of the press,” Mr. Obama said.

But the United States may still find getting its point across in the region, directly or indirectly, a challenge as leaders take a more critical, “get your own house in order” eye to the polarization in Washington and the United States’ own problems with justice.

“These are societies that are not especially responsive to what Washington does or wants, and have not been for a long time,” said Julia Sweig, a Cuba and Brazil scholar at the Lyndon B. Johnson School of Public Affairs in Austin, Tex.

American sway in the region has been undercut somewhat paradoxically by the sweep of democracy since the 1970s and ever more flourishing economies — with the United States typically among the top trading partners. As a result, internal interests now routinely trump regional ones, especially when the United States is perceived as talking-down or resorting to heavy-handed tactics.

In his remarks to world leaders at the summit, Mr. Obama sought to take this on, acknowledging the imperfections of American society but also bluntly telling his peers not to dwell on the past or use the United States as a scapegoat.

“America never makes a claim about being perfect,” he said. “We can, I suppose, spend a lot of time talking about past grievances, and I suppose that it’s possible to use the United States as a handy excuse every so often for political problems that may be occurring domestically.

“But that’s not going to bring progress,” Mr. Obama continued. “That’s not going to solve the problems of children who can’t read, who don’t have enough to eat. It’s not going to make our countries more productive or more competitive in a global economy.”

Still, to its frustration, the United States has watched shades of authoritarianism show up among democratically elected leaders in Nicaragua, Venezuela, Ecuador and even Panama, where the host of the summit, President Juan Carlos Varela, was elected last summer by voters frustrated with the corruption scandals and autocratic control of his predecessor, Ricardo Martinelli.

Until now, any American effort to push for regional consensus on a broad agenda that includes addressing climate change, drug trafficking and economic prosperity has been undercut by its refusal to have relations with Cuba and its isolation of it. Many countries talked a long time about Cuba’s exclusion at previous summits.

“Despite really significant remaining differences in the region, by sweeping aside the Cuba problem I think you are going to see more leaders step up to the plate more on human rights and democracy,” said Arturo Valenzuela, the State Department’s former top diplomat for the region and a professor at Georgetown University.

He predicted regional powers such as Brazil might reward the American reconciliation with a tougher stand on Venezuela; already few countries at the summit outside of Venezuela’s closest allies joined its railing against the recent American sanctions.

Mr. Valenzuela said topics at the summit that received scant attention from the news media, including regional leaders discussing an expansion of economic opportunities, addressing inequality and promoting the work of “civil society” nongovernmental organizations to push for basic freedoms, might rise in importance, even in Cuba.

“As you get more independent civil society they can push more for change from the inside,” he said. “That is where it comes from.”

Eric Hershberg, director of the Center for Latin American and Latino Studies at American University in Washington, said Mr. Obama had been gaining ground in the region. It is not just his reaching out to Cuba but also his executive action on immigration, to allow more people in the country without authorization to get legal residency, he said.

“Now, we will see whether the administration can continue that momentum with engagement in Latin America and focus on the issues the region cares about,” he said.

“The United States,” he added, “needs to avoid getting trapped in unproductive disputes that look like falling back into the old American heavy-handedness in the region.”