The two major parties both selected their nominees through primary elections. Sweitzer, who had also been Democratic Party's 1915 nominee, defeated Thomas Carey, the former chair of the Cook County Democratic Party, in the Democratic primary. Thompson won a large margin of the vote in the Republican Party primary over both Harry Olson, who had also been his opponent in the 1915 primary, and 1911 Republican mayoral nominee Charles E. Merriam.
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