For several decades, the political establishment told Americans that the government is nice and can give them what they want. They did get much from government, but (not surprisingly) also paid much. And ordinary people got their preferences crushed and their lifestyles scorned or controlled by political correctness, the war on smokers and rednecks, and countless regulations. Life became more politicized and conflictual. No wonder that so many people are angry.
Add to this a serious recession, crony capitalism, changes ushered in by technology and international trade (which lifted a big chunk of mankind out of poverty and provided Americans with inexpensive goods from all over the world, but who understands this?), and a failing education system.
Instead of reaching for the liberty that made America great, the crushed people looked for scapegoats and a strongman. But I think the main culprits are to be found in the political and intellectual establishment.