President Barack Obama pledged during the 2012 campaign, and since, that he will not let Iran develop nuclear weapons.
According to his own timeline, Obama has about a year left to see if his policy of diplomacy and sanctions can get Iran to slow its enrichment of uranium and assure the world its nuclear program is peaceful. If the United States and its partners cannot succeed, the stage may be set for an American or Israeli military intervention.
Resolving the standoff while avoiding war ranks among the biggest foreign policy challenges of Obama's second term. And time grows short.
"When it comes to preventing Iran from obtaining a nuclear weapon, I will take no options off the table. ... That includes all elements of American power: a political effort aimed at isolating Iran, a diplomatic effort to sustain our coalition and ensure that the Iranian program is monitored, an economic effort that imposes crippling sanctions and, yes, a military effort to be prepared for any contingency." — Speech to pro-Israel lobbying group AIPAC, March 4, 2012.
"The United States will do what we must to prevent Iran from obtaining a nuclear weapon." — Speech to United Nations, Sept. 25, 2012.
In his last debate with Republican candidate Mitt Romney, two weeks before the election, Obama more explicitly outlined his red line for Iranian nuclear advancement. He drew it at "breakout capacity," or when Iran has acquired the necessary know-how and enough enriched uranium to build a bomb.
"We have a sense of when they would get breakout capacity, which means that we would not be able to intervene in time to stop their nuclear program," Obama said.
Since winning re-election, Obama has pressed on with his two-track Iran strategy of sanctions and diplomacy.
In Kazakhstan in February, the U.S. and other world powers presented Iran with a new offer of eased sanctions for nuclear concessions. But the memory of countless failed negotiations with the Iranian government has participants and observers alike skeptical that a breakthrough can be reached, and almost certainly not until after Iran's presidential elections in June.
The president's recent Mideast trip has taken some pressure off him for an immediate resolution. Burying their previous disagreements, Obama and Israeli Prime Minister Benjamin Netanyahu agreed on the timeline remaining before Iran could build a bomb. The Jewish state's leader also endorsed Obama's efforts and toned down threats of any imminent Israeli military action.
Still, Obama doesn't have much time if he hopes to avert a military confrontation.
Sanctions are destroying Iran's economy but not its will to enrich more uranium. U.N. reports have outlined worrisome research into possible warhead delivery systems. And as Iran gets closer and closer to nuclear weapons capacity, the concern becomes ever graver in Israel — which the Islamic republic has threatened to wipe off the map — and Iran's Arab rivals in the Persian Gulf, such as Saudi Arabia.
The clarity of U.S. intelligence assessments may prove decisive. Iran's nuclear activity remains notoriously opaque despite years of international efforts to pry open sites for inspection. How Obama reacts in the coming months, and possibly years, could largely depend on the degree of certainty the U.S. has on whether any red line has been breached.