Complex sentence: The 9th is a heavily Democratic, majority-African-American district, located entirely within the city of Memphis (no suburban territory) which has been in Democratic hands since 1975; the Republicans have not made a truly serious bid for the seat since 1978.
Split into simpler sentences: The 9th is a heavily Democratic, majority-black district which has been in Democratic hands since 1975. The Republicans have not made a truly serious bid for the seat since 1978.