I suspect that if you got a hammer and some nails and actually managed to fix them to a particular period, it would be immediately post-WW2 up to perhaps Reagan's junta. The thing to do then would be to ask them to identify this period on a graph of top-level tax rates over time. You'd probably find they prefer a period when unions had commanding strength and top-level taxes were in the high 90s of percent. The decline of the American middle-classes was initiated by Reagan.