Preparations are underway Tuesday morning for the announcement of a nuclear deal with Iran, officials in Vienna tell NPR's Peter Kenyon.
The agreement between six world powers and Iran over the country's nuclear program represents a break from decades of strained diplomacy and geopolitical gamesmanship.
The announcement comes at the end a marathon negotiating session that was preceded by a series of deadline extensions over three weeks.
The details of the deal are still emerging but, much like an interim deal did in 2013, it will likely curb some parts of Iran's nuclear program in exchange for a lifting of some economic sanctions.
In a lot of ways, this is far from over: The agreement still has to be approved by various world capitals.
In Washington, where Congress has two months to review the deal, it has been unpopular among Republicans. (If you remember, despite protestations from the White House, Speaker John Boehner invited Israeli Prime Minister Benjamin Netanyahu to speak to Congress against the deal.)
Since the Iranian Revolution in 1979, the nuclear issue has alienated Iran and vexed Western powers. But reaching a sweeping solution has been a foreign policy priority for President Obama.
Beginning with secret talks at the end of 2009, the U.S. and Iran laid the groundwork for an agreement. With a phone call to Iranian President Hassan Rouhani in Sept. 2013, Obama became the first American president to speak directly to an Iranian head of state since 1979.
That phone call opened the door for an interim deal, which was reached in November 2013. The P5+1 (the five permanent members of the United Nations Security Council — U.S., Russia, China, U.K., France — plus Germany) and Iran then reached a framework accord in April. After fits and starts and disagreements over issues that were touched on in that accord, diplomats emerged in Vienna late today saying they were ready to make history.
NPR's Peter Kenyon tells us that it is still unclear what it would mean if the deal were to be rejected by one or more of the parties.
"They could try to set a date for a renewed effort, but as a practical matter, non-proliferation experts say, it would kill the momentum and likely lead to a longer setback," Peter told us. "In 2005, it led to several years of buildup, hostility and sanctions. But there isn't a rulebook for that eventuality."
It also depends on who rejects it. If it's the U.S. or Iran, "it probably means no quick return to the table," Peter says.