Iran and a group of six nations led by the United States said they had reached a historic accord on Tuesday to significantly limit Tehran’s nuclear ability for more than a decade in return for lifting international oil and financial sanctions. The deal culminates 20 months of negotiations on an agreement that President Obama had long sought as the biggest diplomatic achievement of his presidency. Whether it portends a new relationship between the United States and Iran — after decades of coups, hostage-taking, terrorism and sanctions — remains a bigger question. Mr. Obama, in an early morning appearance at the White House that was broadcast live in Iran, began what promised to be an arduous effort to sell the deal to Congress and the American public, saying the agreement is “not built on trust — it is built on verification.” Mr. Obama made it abundantly clear that […]