GENEVA—Iran and world powers expect to announce an initial deal as early as Friday to curb Iran’s nuclear program in exchange for an easing of sanctions, a step that would mark the first breakthrough in a decade to blunt the threat of Tehran developing nuclear weapons. Secretary of State John Kerry will fly to Geneva on Friday to complete the deal, the State Department said. President Barack Obama described the emerging agreement Thursday in an interview with NBC News, saying that if Iran doesn’t live up to its end, “we can crank that dial back up” on sanctions. The two sides were jointly preparing a draft agreement ahead of a likely announcement, said Iranian and Western officials, although the plan could still unravel. The White House already faces major opposition both from its allies in the Middle East and members of Congress. Israel, in particular, has been deeply skeptical. […]