Complex sentence: In an astonishing upset, O'Higgins came within 1% (or 10,000 votes) of defeating de Valera, de Valera left the blame for this with his campaign manager Charles Haughey.
Split into simpler sentences: In an astonishing upset, O'Higgins came within 1% (or 10,000 votes) of defeating de Valera. De Valera left the blame for this with his campaign manager Charles Haughey.