It marked the worst year for manufacturing since 2015, as the trade war, lackluster global growth and problems at airplane maker Boeing hurt America's industrial economy. There were signs of a rebound after manufacturing production rose from July to September, but the latest data show that output fell back into negative territory in the fourth quarter. "Manufacturing is in a slump. It's an export-sensitive sector and exports have been hammered," said Rubeela Farooqi, chief U.S. economist at High Frequency Economics. Economists say manufacturing is no longer the harbinger it once was for overall economic health because the sector accounts for just a little over 10% of the economy. But the sector plays an outsized role in the economies of several politically important swing states, including Wisconsin, Michigan and Pennsylvania, which have all shed manufacturing jobs in the past year.