The Democratic Study Group was a very influential group, which played a key role in changing the House of Representatives. It was founded in 1959 "as a liberal counterpoint to the influence of senior conservatives and southern Democrats". In a June 1974 article by Stevens, Miller and Mann entitled "Mobilization of Liberal Strength in the House 1955-70, The Democratic Study Group" (available via JSTOR), the early years of the DSG are described -
"Although small groups of liberals had been meeting on an ad hoc basis with increased frequency since 1953, the formal organization of the Democratic Study Group (DSG) in September 1959 marked the first sustained effort to counter the conservative coalition. The organizational structure and operating strategies developed in the first few months, aimed as they were at the problems of information, attendance and strategic bargaining, remained remarkably constant over the subsequent decade.
Concerned with increasing the likelihood of liberal policy outputs, the DSG engaged in activities at every stage of the legislative process. But its major focus continued to be providing information necessary to bring some coherence to the liberal Democratic bloc."
Members paid a (substantial) research fee to subscribe - which enabled the employment of a number of members of staff. The paper quoted above reported that - "In practice, virtually all of DSG's activities are generated and executed by the staff, which has assumed an independent leadership role in recent years. The DSG staff ordinarily consists of approximately twelve people, four of whom engage in legislative research. The institutionalization of the DSG has left the staff director a good deal of discretion in initiating and overseeing DSG operations."
A key player was Richard Conlon, the staff director. He spoke about the DSG on a C-SPAN programme in 1988 which can be accessed here. Sadly, Mr Conlon was killed in a boating accident in June 1988.