President Obama came to office in 2009 with a grand plan to reshape U.S. foreign relations through outreach to hostile governments.
In his first term, his overtures to Iran, Russia, Syria, North Korea and others produced limited payoff.
But with his decision to restore diplomatic ties to Cuba, Obama has doubled down on "engagement" and his belief that by opening up to adversaries, rather than isolating them, the United States can sweep away obstacles from years of conflict and move authoritarian states toward Western-style freedoms.
The initiative will open Cuba "in ways that it hasn't been before," Obama said at a news conference Friday. "Over time, that chips away at this hermetically sealed society and, I believe, offers the best prospect of leading to greater freedom, greater self-determination on the part of the Cuban people."
Engagement "remains the core of an Obama doctrine," said Julianne Smith, a former deputy national security advisor to Vice President Joe Biden. "He recognizes that it's not without risks…. But it can produce results."
The administration has now conducted successful negotiations with two longtime adversaries: Iran, for an interim nuclear agreement, and Cuba, to end more than half a century of isolation.
Critics say American incentives give authoritarian governments political legitimacy and an economic boost that will extend their rule, without doing much to help their citizens. Obama conceded Friday that Cuba isn't likely to change "overnight," but he said that after 50 years of failed U.S. policy toward Cuba, it's time to try something new.
That's not likely to mollify Cuba hawks in Congress, such as Rep. Christopher H. Smith (R-N.J.). Rather than bringing the Cuban people closer to democracy and freedom, he said, Obama "is enabling tyranny."
Elliott Abrams, a former deputy national security advisor to President George W. Bush, accused Obama of bailing Havana out of difficulty since the death of leftist Venezuelan President Hugo Chavez, who helped prop up the Cuban economy with cheap oil.
"Today Chavez is dead, oil is under $60 a barrel, and Venezuela is reeling," Abrams, now with the Council on Foreign Relations, wrote last week. "Who will bail Castro out this time? Now we have the answer: Barack Obama."
Obama maintains that exposure to Americans, their ideas and a free economy will gradually take hold in Cuba. By linking Cubans to the rest of the world, the Internet and social media can accelerate the change.
"He is playing a long game," said former Biden advisor Smith, who is now with the Center for a New American Security think tank in Washington.
The risks for Obama are clear.
Though the Castro government freed an imprisoned U.S. spy, and has agreed to release several dozen people the U.S. considers political prisoners and to ease Internet restrictions, it did nothing to ease widespread repression. It could easily embarrass Washington by launching a political crackdown.
The administration's other acclaimed move for diplomatic engagement, in Myanmar, is already in doubt.
The White House began to ease sanctions in Obama's first term after the military government there said it would share power more widely after five decades of authoritarian rule. The two countries restored diplomatic relations in 2012, but Myanmar's democratic reforms have been slow in coming, and human rights groups condemn what they say is ethnic cleansing against the Rohingya Muslim minority.
Prospects also are uncertain for Obama's highest-priority diplomatic initiative, the effort to secure a nuclear deal with Iran.
Early in his first term, Obama sent a personal letter to Iran's supreme leader, Ayatollah Ali Khamenei, seeking better relations. He has now written four letters, spoken by telephone with Iranian President Hassan Rouhani and sent a video to the Iranian public.
U.S. and Iranian military forces are in tacit alignment against Islamic State militants in Syria and Iraq, but the nuclear deal is unfinished despite a year of international negotiations and two blown deadlines. By most assessments, it was tough U.S. and European sanctions, not diplomatic gambits, that brought Iran to the negotiating table.
The early White House attempt to "reset" relations with Russia yielded a few dividends, including the New Start strategic nuclear weapons agreement. But after President Vladimir Putin returned to power in 2012, relations quickly soured.
Putin's government "might have been impossible to get through to with any approach," said Robert Danin, a former U.S. diplomat now with the Council on Foreign Relations.
Administration officials insist, though, that outreach can pay dividends even without a clear breakthrough.
U.S. proposals to Tehran helped convince balky European countries, as well as Russia and China, that the impasse in the Iran nuclear talks wasn't due to American intransigence, U.S. officials say.
"If the U.S. hadn't come to the table in a serious way in 2009, there's no way we could have gotten the United Nations sanctions and built the pressure that's now on Iran," said a senior administration official who spoke on condition of anonymity to discuss sensitive talks.
Supporters of engagement say cutting diplomatic ties to governments generates ill will and disrupts communications at times of crisis.
U.S. administrations have repeatedly imposed embargoes or downgraded relations with Pakistan over its nuclear weapons program and support for several terrorist groups. Those moves alienated Pakistan's public and cut ties to important contacts in Islamabad without changing the government's course.
"In a crisis, you need personal relationships," said Smith of the Center for a New American Security. "You can end up not even having a number to call."