Yemen’s warring political factions were on the verge of a power-sharing deal when Saudi-led airstrikes began a month ago, derailing negotiations for a national unity government, the United Nations mediator said. Jamal Benomar, the U.N. envoy who spearheaded those negotiations until he resigned last week, told The Wall Street Journal the bombing campaign against the Iran-linked Houthi rebels has hardened positions on a key point—the composition of an executive body to lead Yemen’s stalled transition from dictatorship to democracy. This will complicate new attempts to reach a solution, he said. “When this campaign started, one thing that was significant but went unnoticed is that the Yemenis were close to a deal that would institute power-sharing with all sides, including the Houthis,” said Mr. Benomar, a Moroccan diplomat. […]