Zimbabwe’s ruling party, bent on retaining control after 28 years in power, has broadened its campaign of intimidation and violence to include teachers and even aid workers, disrupting education and basic care for tens of thousands of children across the country, according to humanitarian groups, union officials and the teachers themselves. Teachers have been upbraided by the ruling party for allegedly siding with the opposition during the nation’s disputed March elections, in which they served as poll monitors. More than 2,700 of them have fled or been evicted from classrooms, the teachers’ union says.