Thomas Edsall has a round-up of recent polls and studies on who supports Trump and why, which I recommend. A couple of points:
1) The economic group that has moved most strongly toward the Republicans under Trump is white people with household incomes above the 60th percentile (currently $77,000/year) but without college degrees. This is now the Republicans' strongest socio-economic group. However, they have fallen from 42.1 percent of white voters 60 years ago to 22.0 percent. These people – skilled construction workers, factory supervisors, small business owners -– are the conservative backbone in America.
2) White evangelical voters are less racist than other groups of Trump supporters, however you measure racism. (This confirms my experience; very religious Christians often have warm feelings about other Christians of any race, and there is a fair amount of minister swapping between black and white congregations and things like that.) Yet, white evangelical voters are more enthusiastic in their support of Trump than non-religious Republicans. Edsall doesn't try to explain this, but I would point to two things. I suspect evangelicals are just stronger in their attachments to abstract causes than non-religious people, so once they take a side they support it with less hesitation. And, evangelicals feel themselves besieged in an increasingly secular America and think they need a fighter like Trump to defend them.