There was a large complacent middle class from the very beginning of America... Only about a third of the country, led largely by the upper class, whom had the most to gain but also the most to lose, wanted to revolt against England. Another third, again, largely led by the upper class that were scared to lose, wanted to continue our relationship with England. The final third didn't really care, they just wanted to be left alone to do their thing.
Anyway, at the time, we had the very wealthy - large plantation owners, the very poor - slaves, indentured servants and the like, and a large middle class made up of independent businessmen and the help they hired. That held true up until the 20th century, when the government decided that it needed to become involved in the business of redistributing the wealth as a reaction to the extreme wealth created by the industrial revolution, largely due to a fad regarding Marx, Engels and such.
The post-WWII boom wasn't created by the policies of Wilson, FDR, LBJ or whatever progressive hero you have, it was created by the simple fact that most of the factories in the rest of the industrial world were destroyed by war and Europe, Eastern Asia and the like had to rely on the unscathed factories of the United States and Canada to rebuild. It was only natural that, as the manufacturing capacity of Europe and Asia were rebuilt, that the United States would decline. You've been trained to blaim the policies of Nixon, but it was simply the duration of the rebound of the first world economy outside of the Americas.
What we had done in the meantime, was create numerous entitlement programs which, especially regarding the Great Society, were unsustainable. Specifically in the case of the Great Society, with welfare, Medicaid, Medicare and the like, Congress decided to raid the Social Security Trust Fund (via an Amendment in 1967) to paper over the huge costs, which had far exceeded CBO projections prior to passage. The truth is, in addition to taxes, inflation, and bonds, Congress was raiding the other "lock boxed" source of income, largely so they could continue to lie to people, telling us that we could afford something they already knew would bankrupt us. They lied and they were either retired or dead before people began to catch on - but they got to stay in office longer, having duped the masses.
So, by all means, blame Nixon. Blame Ford, Reagan, Bush and Bush if you want to... but be sure to blame Obama, Clinton, Carter, LBJ, JFK, Eisenhower, Truman, FDR, Hoover, Wilson and TR too, since they all contributed to our current problems in their own way. Don't be a partisan hack and pretend all the problems fall on one side or even one President, because they were all involved. More importantly, don't forget their Congresses, since the President can't introduce legislation on their own and all spending, in particular, must originate in the House.
Be sure to blame the unions too... for demanding more than what was responsible in the long term, but like the 1967 Congress that authorized raiding the Social Security Trust Fund, blame the union leadership for cashing in on what they knew was unsustainable so they could maintain and grow their own power, influence and pocketbooks. Likewise, blame the executives that capitulated to them.
Under the guise of redistribution of wealth, you end up with two classes - the rich that have the money to defend themselves, and the poor, who demand everything from anyone else. It's the middle class, which has enough money to provide for themselves but not enough money to defend themselves, that suffer from the powers that demanding wealth redistribution, be it the government or the special interest groups that advocate it. It's also the natural result of converting the government from a body solely meant to protect our rights into a body out to seek reparations from one group on behalf of another.