Out of control immigration was the real catalyst. The country is simply being given away.
The combination of a massive welfare state with unprecedented levels of immigration has not gone unnoticed by the average citizen. Why is a country obligated to take in masses of mostly uneducated third world migrants because there are jobs Americans "just won't do". Meanwhile there is a large portion of the homegrown population collecting benefits.
Working Americans are forced to pay for services to accommodate the new arrivals and are then called racist/ xenophobic if they question it. 
Our schools constantly complain that they are underfunded and yet they still have the money for funding increases of bilingual education, low income meals, and more. If your own kid needs a math tutor, you pay for it yourself. 
Same with  medical services. Everyone gets treated, the ''system" picks up the added cost.
The average citizen has begun to feel as if they are paying for their own displacement.