WHY is that?
I don't agree that physicians are mostly liberals. However, much of the influence is the same for physicians and nurses, except for the unions.
Several reasons why a lot of nurses are liberals. First, the influence of liberal college nursing instructors is great, as they tear down your self esteem and rebuild it via an aggressive and exhaustive curriculum. Second, the heavy influence of unions on the nursing profession. Third, it is a service industry focused on assisting the infirm, drawing liberal types. Same with social workers.