WASHINGTON — President Barack Obama is finding stern challenges at home to his foreign policy, facing hard sells to skeptics over US breakthroughs on Iran and now Cuba. Obama returned to Washington on Sunday still basking in the attention from his historic meeting with Cuban President Raul Castro at the Summit of the Americas. But Obama is certain to find a less appreciative crowd in Congress, whose support he needs to complete a nuclear agreement with Iran. Cuba and Iran offer Obama, whose term ends in early 2017, the potential for legacy-crowning achievements. Iran may prove a greater challenge than Cuba, but together they are subjecting Obama's foreign policy to the kind of scrutiny that most international issues, short of war, rarely draw. Obama made clear in a closing news conference Saturday in Panama City that he believes he can handle the twin trials. The American public is on his side on Cuba, the president said, and he had tough words for Republicans defying him on Iran. Both issues have roots in decades of grievances. Both have had constituencies in the US deeply mistrustful of the governments with which Obama is dealing. Pro-Israel Americans cannot fathom a deal with an Iran that will not recognize Israel's existence. And for decades, Cuban-Americans who escaped Fidel Castro's revolution could not imagine a US government not committed to ousting the Havana government. But Cuba is hardly the threat Iran could be. Public opinion no longer demonizes Cuba. “The American people don't need to be persuaded,” Obama said. Still, there are reminders that the barriers have not all fallen. The room where Obama and Castro met displayed no flags, a reminder of the absence of diplomatic relations. Obama's next step is removing Cuba from the United States' list of state sponsors of terrorism. Such a decision, recommended by the State Department, could come in days. Obama would have to notify Congress. Lawmakers do not have to ratify the decision, but they have 45 days to disapprove it. The White House hardly appears worried about the politics of Cuban diplomacy, given that support for ending more than 50 years of US isolation of the island nation crosses party and geographic lines. Obama perceives the Iran deal as far more fragile. Iran and the world powers negotiating the agreement have until the end of June to reach a final deal, and the Iranian leadership has a distinctly different interpretation of what the sides have settled on so far. Congress is angling to assert authority over the final agreement. Obama reserves most of his frustrations for Republicans, and he singled out Sen. John McCain, his 2008 presidential rival, for scorn during Saturday's news conference. McCain last week declared a major setback in the nuclear talks after Iran's supreme leader demanded that sanctions against Tehran had to be lifted immediately after a deal went into place. Obama cast McCain's criticism as an assault on the credibility of Secretary of State John Kerry. “Now we have a senator suggesting that our secretary of state is purposefully misinterpreting the deal and giving the supreme leader of Iran the benefit of the doubt in the interpretations,” Obama said. “That's not how we're supposed to run foreign policy, regardless of who is president or secretary of state.” — AP