Is it because the economy isn't doing all that great? Then blame corporate America. They are the ones shipping jobs overseas and putting profit before people. Yet any attempt to somehow level the playing field is socialism and anti-capitalism, things the Republicans hate. Is it because we now have gays in the military and gays are getting married? Funny. I haven't seen any Nazis riding dinosaurs lately. The world hasn't ended. Schools haven't closed because there is an epidemic of gayness. Is it because we're not out there with 100,000 boots on the ground kicking terrorists' asses? Why would you want to put American lives at risk in the butthole of the world? Obama is weak? Funny. He has killed more terrorists than any other president in history. Perhaps he realizes that the Middle East is a quagmire, and the best strategy is to sit back and watch radical Muslims kill other radical Muslims over there.
The only thing I can think of in terms of what would be "greatness" is that we are no longer The United States of Jesus. "Greatness" is a really a euphemism for Christian morality. The Church is losing its grip on power. When you watch tv shows or movies from the early part of the last century, everyone went to church on Sunday. People have slowly become smarter and wiser and have given up that old dogma of following exactly what The Church wanted. It has become a less important factor in many of our lives. Free and open thinking have also allowed more progressive ideas of human rights. Would we be having conversations about transgendered people in the 1950's? Would there be talk about other religions besides Christianity? OK. We'll allow the Jews (even though they killed Jesus!)
So when candidates start talking about going back to the "good old days," you have to stop and think about just what was good about them.