Table schema:
CREATE TABLE table_2668336_19 (incumbent VARCHAR, candidates VARCHAR, result VARCHAR)

Question: Who were the incumbent(s) in the election featuring  john murray (dr) 50.4% george denison (dr) 49.6% with a result of a retired democratic-republican hold?
SQL: SELECT incumbent FROM table_2668336_19 WHERE candidates = "John Murray (DR) 50.4% George Denison (DR) 49.6%" AND result = "Retired Democratic-Republican hold"