Background The rapid diffusion of social media in the past decade has allowed community members to sway the discourse on elections. We use analyses of social media to provide insight into why the strong public support 1 year prior to the election did not result in an increased tobacco tax from the 2012 California Proposition 29 vote.

Methods Using the Twitter historical Firehose, we chose all tweets on Proposition 29 posted between 1 January and 5 June 2012 differentiating between early and late campaign periods. Tweets were coded for valence, theme and source. We analysed metadata to characterise accounts. Television ratings data in 9 major California media markets were used to show the strength of the 2 campaigns.

Results ‘No on 29’ launched television advertising earlier and with much higher household gross rating points (GRPs) than the ‘Yes on 29’ campaign. Among 17 099 relevant tweets from 8769 unique accounts, 53% supported Proposition 29, 27% opposed and 20% were neutral. Just under half (43%) were from accounts affiliated with the campaigns. Two-thirds of campaign messages originated outside California. The ‘Yes’ campaign focused on simple health messages, which were equally represented in both campaign periods. However, anti-tax tweets increased at relative to pro-tax tweets in the second period.

Conclusions Although the Prop 29 campaigns did not effectively engage the Californian twitter communities, analysis of tweets provided an earlier indication than public polls of the loss of public supporting this election. Prospective Twitter analysis should be added to campaign evaluation strategies.