Saw this interesting data about the political affiliations of various occupations. http://verdantlabs.com/politics_of_professions/
Some were expected:
1) Environmentalists are strongly Democrat, while oil workers are strongly Republican.
2) Union organizers are strongly Democrat, while business owners are strongly Republican.
But others were unexpected:
1) Psychiatrists are strongly Democrat, while neurosurgeons are strongly Republican.
2) Architects are strongly Democrat, while home builders are strongly Republican.
3) Carpenters are strongly Democrat, while plumbers are strongly Republican.
It appears that certain professions attract people having particular values, and that these values correlate with political affiliation. Or, it could be that once a person is established within a particular profession, the experiences he encounters cause him to lean towards one or the other party, either for economic reasons or for values-based reasons.