PHOENIX — As they packed up their protest signs and returned to the classroom to finish out the school year, thousands of teachers in North Carolina turned their attention to a different fight: the midterm elections. Their counterparts in Arizona, Oklahoma and West Virginia are already waging a similar battle following protests over teacher pay that shut down schools statewide in recent months, transforming education funding into a major midterm campaign issue in many states. Leaders of the Arizona movement are gathering signatures for a ballot initiative to tax the wealthy and use the extra money to pay for education.