Breaking from two decades of tradition, this year’s election exit poll is set to include surveys of voters in 31 states, not all 50 as it has for the past five presidential elections, according to multiple people involved in the planning. Dan Merkle, director of elections for ABC News, and a member of the consortium that runs the exit poll, confirmed the shift Wednesday. The aim, he said, “is to still deliver a quality product in the most important states,” in the face of mounting survey costs. Voters in the excluded states will still be interviewed as part of a...