Complex sentence: She chaired the 1988 presidential campaign of Gary Hart in 1987 until his withdrawal, at which point she briefly entered the race, before announcing her own withdrawal in an emotional press conference on September 28,1987.
Split into simpler sentences: She chaired the 1988 presidential campaign of Gary Hart in 1987 until his withdrawal. She then ran for President of the United States, before announcing her own withdrawal in an emotional press conference on September 28,1987.