So far, there have been no discussions between Mr. Biden’s representatives and the Russians about the treaty, transition officials said, because of what Mr. Sullivan referred to as the tradition of “one president at a time.”
Conversations four years ago between the Russian ambassador to the United States and Lt. Gen. Michael T. Flynn, Mr. Trump’s first national security adviser, led to the initial investigations of the administration’s dealings with Russia. Mr. Biden’s team said it was scrupulously avoiding contact with foreigners on any issue of significance until the afternoon of Jan. 20.
The idea of moving forward with a separate agreement with Iran on missiles is not new, but Mr. Trump made no effort to negotiate any limits after pulling the United States out of the nuclear accord in mid-2018.
Mr. Sullivan and Daniel Benaim, who was a Middle East adviser to Mr. Biden when he was vice president, argued in a Foreign Affairs article in May that the United States should, under a new president, “immediately re-establish nuclear diplomacy with Iran and salvage what it can from the 2015 nuclear deal,” and then work with allies and Iran “to negotiate a follow-on agreement.” At the same time, the United States would support what they called a “regional track” of negotiations that would include Saudi Arabia, Iran’s chief rival in the region, and one of the main targets of its missile program.
Any effort to resuscitate the Iran deal will undoubtedly open a new breach with Republicans, who have already argued that Mr. Biden was tied to a flawed nuclear accord. But the deal was never a treaty — it was an executive agreement, which Mr. Trump abandoned by declaration — and its restoration could also be done by executive order.
The key question is whether the Iranians are willing to go back to the old deal. It was widely unpopular in the country, where many believed that the United States never intended to allow Tehran to enjoy its economic benefits. And Iran is about to plunge into a presidential election of its own, in which a hard-line Air Force officer from the Islamic Revolutionary Guards Corps is one of the leading candidates. Re-entering the limits of the existing deal, without extracting some kind of reparations from the United States for Mr. Trump’s decision to reimpose sanctions, may be politically impossible before the election.
When pressed by his interviewer, Fareed Zakaria, on why the 2015 deal did not bring about an easing of tensions and new cooperation with Iran, Mr. Sullivan rejected the idea that the Obama administration had expectations beyond limiting the nuclear program.