Not since at least 1980, when the United States was reeling from the oil shocks, inflation and slow growth of the previous decade, has the economy been in worse shape heading into the heart of a presidential campaign. The crush of bad economic news — six consecutive months of job losses, rising rates of home foreclosures, gasoline prices seemingly headed toward $5 a gallon — is increasingly setting the contours of the race between Senators Barack Obama and John McCain.