In fact, looking at this graph, you see that the median income did not increase at all between around 1978 and around 1993. Much like it's stagnated between 2000 and now. That increase by 1.25 times that did occur almost entirely took place in the mid- and late nineties.
Coincidence that it was the Reagan, Bush Sr and Bush Jr administrations that was middle-class income stagnate even as GDP kept growing? Or the consequence of Reaganomics and its offspring?
Two different paragraphs to be commented.
The median income DID increase during the period 1978-1993, unless you want to look only at both ends of the 1978-93 graph. It certainly increased less than productivity and less than GDP, but during most of the years in that span, income was higher than at the beginning.
Of course it's a consequence of Reaganomics. But we must understand that Reaganomics didn't come out of nothing.
During most of the early post-war, American wages grew according to productivity. This also meant that profits could increase only by increasing productivity. As classical industries (typically, steel) struggled to increase productivity, and as other industries (typically textiles and electronics) fragmented their production and "exported" its labor-intensive segments to countries with cheaper labor, the whole system stagnated, with bad returns for both investors and workers (the Carter years).
What Reaganomics (and Thatcherism) did, in first place, was to break the back of the workers' unions. This easied the transfer of labor-intensive segments both within the US borders (from unionized states in the North to non-unionized stated in the South) and outside the borders. And easied a dynamic transformation of the American economy, away from the classical industries and much more into services and new types of industries (think Silicon Valley).
In this sense, the limited view of unions helped Reaganomics and Reaganpolitics. Instead of proposing a new social deal (a definition of class wealth distribution, that would have meant some sacrifices, but not the complete loss of power) they just fought for the rights (and privileges) of their members. And lost handily.