Complex sentence: Undaunted by his earlier setbacks, in 1970, Andrus defeated Samuelson in a gubernatorial election rematch, thanks in large part to his opposition to developing molybdenum mining in central Idaho's White Cloud Mountains.
Split into simpler sentences: Undaunted by his earlier setbacks, Andrus successfully defeated Samuelson in a gubernatorial election rematch in 1970. This was attributed in large part to Andrus'public opposition to developing molybdenum mining in central Idaho's White Cloud Mountains.