The GOP kept cutting taxes on the rich - but supply side trickle down economics only works if the rich use their tax savings to spend and invest inside the USA. When globalization happened in the 90s the rich invested their tax savings overseas in China and deposited the profits in overseas banks. So the rest of the population did not see any significant economic growth - that is why I think wages of shrunk or become stagnate.
Only Trump, among all the candidates, has introduced and then pounded on this point. (May God bless him.)