[3] Cook County Clerk Robert Sweitzer challenged incumbent mayor Carter Harrison IV in the Democratic primary.

[6] After the a successful 1912 election cycle for Democrats, a significant number of people had been willing to run for mayor as candidates for Sullivan's faction of the party.

[6] Harrison was accused of being disloyal to the party for not having supported Sullivan's 1914 United States Senate campaign.

[6] He was also painted as an "aristocrat", which was charge that was off-putting to the city's many recent European immigrants, who poorly regarded aristocracy.

[6] Harrison additionally managed to secure a tepid endorsement from Governor Edward Fitzsimmons Dunne.

[6] However, in 1915 this was less effective than it had been four years prior, with the Democratic Party having only months before had Sullivan as its standard-bearer in the state's U.S. senate election.

He ordered police to stop the mass posting of election posters, a favorite campaign tactic of Sullivan's faction.

[6] He also attempted to convince county judge Thomas F. Scully to order every voter in the primary to be challenged.

[6] Scully, a Sullivan ally, voiced distain for this request and alleged that it would amount to voter suppression.

[6] Harrison managed to secure the backing of the United Societies for Local Self-Government, the top pro-alcohol lobbying group.

Sweitzer's victory effectively cost Harrison the opportunity to further pursue a, then-unprecedented, sixth term as mayor.

[5][10] The power balance in Illinois' Republican Party had also been altered by Lorimer's removal from the United States Senate and Deneen's 1913 loss in his bid to seek reelection as governor.

[9] Lundin orchestrated a "draft" effort in December 1914 to demonstrate popular support for Thompson's candidacy.

[6] This would prelude the neutral stance on World War I and the evocation of anglophobia that would become notable characteristics of Thompson's political career.

[6] William Hale Thompson, in turn would later endorse Charles M. Thomson's subsequent successful campaign for the Circuit Court of Cook County later that year.

[6] A major blow to Sweitzer's campaign occurred when, bitter over his loss in the primary, Carter Harrison IV endorsed Thompson.

[5][10] He managed to draw large to his rallies, employing techniques such as putting on parades and circuses to lure spectators to his political events.

[18] Democrats played up the fact that Sweitzer was of Irish and German descent in hopes that it might drum-up enthusiasm amongst voters in Chicago's immigrant community.

[9] Whether or not these charges were true, many Protestant ministers were persuaded by these allegations to publicly support Thompson over Sweitzer.

He made an issue of the low property taxes Daily News publisher Victor Lawson reportedly paid on his Lake Shore Drive mansion.

[19] They undertook misguided efforts to drum up German support for his candidacy, which ultimately proved to be at the peril of his overall appeal to non-German/Austrian voters.

[19] Materials supporting Sweitzer had been distributed in the German and Austrian neighborhoods of Chicago baring images of Kaiser Wilhelm and Emperor Franz Joseph were distributed urging all citizens of central European origin to support Sweitzer and the "Fatherland".

[9] This became significant when Sweitzer did not disavow these materials, thus lending credence to an informal association of him with the Central Powers war effort.

[9] Thompsons campaign seized on this, and distributed identical materials to Chicago's Polish and Czechoslovakian neighborhoods.

[6] Thompson sought to resurrect the, decades old, Ogden Gas Scandal, advertising the fact that Roger Sullivan had now made a significant profit from the company's 1913 sale to the city's local utility monopoly.

[6] Democrats countered this by revealing that Thompson had received a $5,000 contribution from James A. Patterson, the Maning director of the People's Gas and Electric Company.

While Thompson had secured a lead in the campaign, with betting odds reflecting this, people failed to forecast a landslide victory.

[20] In terms of the number of votes, Thompson's margin of victory was greater than any prior Chicago municipal election.

[9] Harrison argued that the critical mistake that Democrats had made was bringing religion into the election and the allowing the circulation of materials containing the likeness of Kaiser Wilhelm and Franz Joseph.

[9] Analysis, however, has shown that Harrison's own endorsement of Thompson was likely a decisive factor in determining the outcome of the election.