For all of the cautious optimism surrounding the framework agreement, some of the toughest issues lie ahead, and the deal could still fall apart.

© Arash Khamooshi/Polaris for The New York Times

While the president says the agreement with Iran would open the Strait of Hormuz and provide economic relief, the country’s nuclear program is still a subject for negotiation.

© Eric Lee for The New York Times

While the president says the agreement with Iran would open the Strait of Hormuz and provide economic relief, the country’s nuclear program is still a subject for negotiation.

© Eric Lee for The New York Times

Britain’s Defense Ministry said it was the first time that British forces had acted alone to stop a ship in the fleet, a collection of vessels that Russia uses to move fuel and evade sanctions.