Aides to Mr. Obama say that Mr. Samore has favored offering Tehran warmer relations with the United States, including lifting certain American sanctions against Iran and assuring the Iranian leadership that the United States will not pursue regime change. (Vice President Joseph R. Biden Jr. said in the past that he thought the United States should assure Iran that it would not pursue regime change.) But Mr. Samore has also argued that such an offer is not enough unless it comes backed by the threat of stronger sanctions from the United States, Europe, Russia and China, like, for instance, a ban on foreign investment in Iran’s oil and gas industry.