The four states pivotal to electing Donald Trump occupy special ground on America’s electoral map, right on the fault line where the political and economic priorities of the East meet the concerns and sensibilities of the nation’s old industrial core. Between the Democratic Party and the voters of Pennsylvania, Ohio, Michigan, and Wisconsin there was a failure of understanding in 2016, and Trump emerged as the answer. Will that history repeat in 2020? The Globe dispatched reporters all over this varied, fascinating, and critical turf to seek the stories of people and communities and explore what may have changed for them since the last election. Read the full 10-part series as an e-book.