Wendy Sherman, the chief U.S. negotiator with Iran, said Wednesday she plans to leave the Obama administration after a June 30 deadline to strike a final deal on curbing the country’s nuclear program. “It’s been two long years,” said the 65-year-old, who is No. 3 at the State Department. After Sherman’s departure, all of the top officials who have negotiated with Tehran over the last two years will have left the administration, raising concern over who will help carry out a deal if one is made by the deadline. Sherman said she did not plan to take another post in the administration.