I’m pretty sure the text tells you, prior to the 1980’s, but they probably mean more the 50’s and 60’s, the 70’s was definitely a down economic era in the US.
Reagan’s administration did a lot of de-regulation, privatization, and cost cutting that are causing now catastrophic consequences on the country. Clinton also screwed the pooch with the NAFTA agreement , Nixon never found a union he didn’t want to crush, we can keep going like this about the screwing of the middle class by other presidents, but none were more destructive and consequential than Reagan.