Follow up to The executive class supports John McCain, see What your work is and how you vote:
Professionals (doctors, lawyers, and so forth) and routine white collar workers (clerks, etc.) used to support the Republicans more than the national average, but over the past half-century they have gradually moved through the center and now strongly support the Democrats. Business owners have moved in the opposite direction, from close to the national average to being staunch Republicans; and skilled and unskilled workers have moved from strong Democratic support to near the middle.
Please see the original post for an illuminating chart....
