In the 70s the Republican Party realized it had the following messaging problem.
How can we reduce the tax and regulatory burden of the donor class, especially given the postwar consensus for Big Government (which includes labor laws for a "living wage", infrastructure investment, subsidies for affordable education and a whole universe of policies that lowered the middle class cost of living - from housing subsidies to anti-trust legislation to transportation subsidies and Fed policies that stimulated the economy during downturns in order to maintain high employment).
In short, in order for wealthy people to extract more benefits and resources from Washington (in order for them to turn Washington into a subsidy and bailout machine for concentrated wealth), they had to convince Americans that government was evil and incompetent - thus undermining government's ability to tax & regulate.
Meaning: in order to re-educate citizens and alter longstanding institutions, the Rightwing created the most powerful and well-funded network of Think Tanks & Media Assets in American History.
Huge incentives were bestowed on anyone who could convince Americans that their Government - which just defeated the Nazis, put a man on the moon and built the most technologically advanced industrial infrastructure in world history - was evil and incompetent.
Not only did they produce an arsenal of paid-for-facts and talking points, but they attracted people to the movement using the culture war (values, religion, patriotism, race and revanchism, e.g., your country has been stolen by "outsiders", and those outsiders have infected your party - therefore we need a straight talking savior who is going to kick Washington's Ass and make it work again...).
Trump has harvested this anger. He doesn't need to know policies or stand for anything in particular. He need only mimic the anti-government rhetoric that the Rightwing Machine has spent 30 years creating. In a more perfect union, the voter would smell bullshit.