Complex sentence: His run for mayor of Jersey City, New Jersey was in 1907 against the Republican incumbent Mark M. Fagan and he stayed in office until 1912 when he lost to Frank Hague.
Split into simpler sentences: His run for mayor of Jersey City, New Jersey was in 1907 against the Republican incumbent Mark Fagan. Whitpenn remained in office until 1912 when he lost to Frank Hague.