Sentence:  Chauncey Depew , one-time runner-up for the Republican Presidential nomination , was attending a convention at Saratoga , where he was scheduled to nominate Colonel Theodore Roosevelt for Governor of New York when he noticed that the temporary <WSD>chairman</WSD> was a man he had never met . 
Meaning of the word marked with <WSD> tags:  the officer who presides at the meetings of an organization