Complex sentence: He had agreed to serve as Lyndon Johnson's campaign manager in 1968 just before Johnson's withdrawal on March 31, and later took over as the campaign manager for the Democratic nominee Hubert Humphrey in his race against Republican Richard Nixon for the presidency.
Split into simpler sentences: He had agreed to serve as Johnson's campaign manager in 1968 just before Johnson's withdrawal on March 31. Sanford later took over as the campaign manager for the Democratic nominee Hubert Humphrey in his race against Republican Richard Nixon for the presidency.