During a 2007 campaign debate when his White House prospects still seemed mostly like a pipe dream, Sen. Barack Obama of Illinois was asked if, as president, he would sit down to talk with leaders of countries like North Korea, Venezuela, Iran and Cuba. "I would," he bluntly replied.

On Tuesday night, seven years later, President Obama finally carried out at least part of the pledge of Candidate Obama, talking with Cuban leader Raul Castro for 45 minutes by phone to put the finishing touches on 18 months of secret negotiations that restored diplomatic relations between the two countries for the first time in over five decades.

The process was carried out under an extraordinarily effective shroud of secrecy. "I hadn't heard even the tiniest buzz that anything was up," one senior State Department official who follows Latin American affairs confessed Wednesday after the president's announcement.

In the clamor for the details of the agreement, which ranges from the number of cigars American visitors can bring home from Cuba to a spy swap involving a convicted murderer and a mysterious and unnamed CIA agent, relatively little has emerged about the negotiating process.

But interviews and statements throughout the day by officials in Washington, Havana and countries that lent aid to the process offer at least a glimpse of the road that led to the historic agreement.

Cuba seemed to drop off President Obama's radar during his first term in office, aside from his occasional public complaint about the arrest of USAID official Alan Gross, charged with crimes against the Cuban state for distributing satellite phones to the island's Jewish community.

But White House officials said Obama ordered a top-to-bottom review of U.S. policy toward Cuba after winning reelection in 2012. By June of 2013, talks between the two countries were under way, led on the U.S. side by Ben Rhodes, the president's deputy national security for strategic communications, and Ricardo Zúñiga, National Security Council senior director for the Western Hemisphere.

At least seven meetings took place in Canada. "I don't want to exaggerate Canada's role," Prime Minister Stephen Harper told the Canadian Broadcasting Corp. "We facilitated places where the two countries could have a dialogue and explore ways on normalizing relations. We were not trying in any way to direct or mediate the talks. We just wanted to make sure they had the opportunity to have the kind of dialogue they needed to have."

But the host of two other meetings played a more active role. The Argentine-born Pope Francis not only welcomed the negotiating teams to the Vatican, he issued an extraordinary "personal appeal" for better relations in personal letters sent to Obama and Castro after a meeting last spring.

Their reaction was positive enough to schedule another meeting at the Vatican, where the deal was sealed. "The Holy See received delegations of the two countries in the Vatican last October," said a Vatican statement issued Wednesday, "and provided its good offices to facilitate a constructive dialogue on delicate matters, resulting in solutions acceptable to both parties."

Both leaders thanked the pope Wednesday. He "played a very important role," Obama told ABC News, calling Francis "the real deal, a remarkable man."

Much remains unknown about the talks, including who negotiated for the Cubans and whether they were carried out with the blessing of Raul's 88-year-old brother Fidel, who ran the country for 50 years until his retirement in 2008.

The irascible Fidel torpedoed several attempts at rapprochement between the United States and Cuba during his rule, notably by sending troops to Africa in the midst of negotiations with President Ford's secretary of state, Henry Kissinger, in the mid-1970s and unleashing a wave of 100,000 refugees on Florida in 1980, soon after President Carter restored partial relations between the two countries.

The ill health that forced Fidel to step down has continued to take a toll, and the extent of his influence on the Cuban government and even the degree of his lucidity these days is unknown. Cuba watchers are waiting to see if he makes a statement about the agreement with the United States.

"If Fidel does not come out and endorse this fully, you've got to wonder what's going on," said Brian Latell, a senior research associate at the University of Miami's Institute for Cuban and Cuban American Studies and formerly the CIA's top Cuba expert. "Is this being done over his objections? Or is he completely comatose?"

Also shrouded in mystery: the identity of a spy being freed by Havana as part of the agreement. "We have decided to release and send back to the United States a spy of Cuban origin who was working for that nation," Raul Castro said during his televised announcement of the deal Wednesday.

"We recovered a highly valued intelligence asset, probably the most highly valued intelligence asset on Cuban soil in American history," confirmed White House Press Secretary Josh Earnest at a news briefing Wednesday. "And that individual is now on American soil."

A statement released by the office of National Intelligence Director James Clapper said the spy "provided the information that led to the identification and conviction" of the so-called Wasp Network, the ring of Cuban intelligence officers arrested in South Florida in 1998. (Three convicted members of the Wasp Network were released by Washington Wednesday, the other half of the swap.)

His information also helped identify three other Cuban spies in the United States: Defense Intelligence Agency (DIA) senior analyst Ana Belen Montes, former Department of State official Walter Kendall Myers and his spouse Gwendolyn Myers.

Those clues led some retired U.S. intelligence officials to speculate that the man released Wednesday by Havana is 51-year-old Rolando Sarraff, a former Cuban intelligence agent arrested by the Castro government in November 1995.

"He's the only one who really fits those details," said Chris Simmons, a former Defense Intelligence Agency spycatcher who specialized in Cuba.

Former intelligence officials say Sarraff was a cryptography expert for Cuba's Interior Ministry who, with two others, passed huge amounts of information to the CIA that allowed Washington to break Cuban spy codes, read their reports, and identify and arrest them. "He just destroyed their communications," Simmons said.

But Sarraff and two other men helping him eventually fell under suspicion. Noting Cuban government surveillance, they sent a message asking the CIA to rescue them. Two of the men were extracted from Cuba. (One, José Cohen, lives in South Florida, where he's a top Amway salesman. He did not respond to Herald emails asking for comment. The other has never been publicly identified.)

Sarraff, however, was arrested and has been in prison ever since. "And at Cuban intelligence headquarters in Havana, a film of those guys leaving the message for the CIA to come to the rescue has been used in training ever since," Simmons said.

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