A perfect storm.
(1) essentially uncontrolled, unfettered legal and illegal immigration; HxB abuses; outsourcing, insourcing; visa overstays
(2) global villagers; level the world playing field; America is a bully; NAFTA, TPP; those jobs aren’t coming back politicians
(3) Silicon Valley and VCs apparently obsessed with automation, and putting people out of work; there are many other problems in the world, and many to be solved quite profitably
(4) increasingly stringent labor and environmental regs in the US especially as compared to some other countries that throw “stuff” in the air and water with abandon and still practice forms of slavery
The US Middle Class finally says, hey what about me? I’m getting hammered here. Believe it or not, they are branded as racist, xenophobic and other ists and ics in response!