Complex sentence: Stagg was seeking to fill the seat being vacated by long-term Democratic incumbent Jack P.F. Gremillion, a protégé of the late Earl Kemp Long, who had been eliminated in the 1971 party primary because of corrupt practices in office.
Split into simpler sentences: Stagg was seeking to fill the seat being vacated by long-term Democratic incumbent Jack P.F. Gremillion, a protégé of the late Earl Kemp Long. Gremillion had been eliminated in the 1971 party primary because of corrupt practices in office.