Emilio Depetris-Chauvin suggests a possible answer:
Using monthly data constructed from futures markets on presidential election outcomes and a novel proxy for firearm purchases, this paper analyzes the response of the demand for guns to the likelihood of Barack Obama being elected in 2008. Point estimate suggests the existence of a large Obama effect on the demand for guns. This political effect is larger than the effect associated with the worsening economic conditions. This paper presents robust empirical evidence supporting the hypothesis that the unprecedented increase in the demand for guns was partially driven by fears of a future Obama gun-control policy. Conversely, the evidence for a racial prejudice motivation is less conclusive. Furthermore, this paper argues that the Obama effect did not represent a short-lived intertemporal substitution effect, and that it permanently affected the stock of guns in circulation. Finally, states that had the largest increases in the demand for guns during the 2008 election race experienced significant changes in certain categories of crime relative to other states following Obama’s election. In particular, those states were 20% more likely to experience a shooting event where at least three people were killed.