Tuesday’s elections were described by some as the “marijuana midterms” even before the first votes were cast. The results lived up to that moniker, as Alaska, Oregon and Washington, D.C., voted to legalize marijuana for recreational use.

Before residents of Colorado, Washington state, Alaska, Oregon and Washington, D.C., voted for legalization in 2012 or 2014, though, California was on track to become the first legal marijuana state in 2010. Indeed, the Golden State’s Proposition 19 — the Regulate, Control & Tax Cannabis Act — was up by seven and 11 points respectively among likely voters in the venerable Field and Public Policy Institute of California (PPIC) polls just over a month prior to the 2010 election. By late October 2010, however, those numbers had reversed: Prop. 19 trailed by seven- and five-point margins in the Field and PPIC polls. The initiative failed by a seven-point margin on Election Day.

The declining support for Prop. 19 from late September to November 2010 coincided with strong statements of opposition from several prominent Democrats. Perhaps most notably, Attorney General Eric H. Holder Jr. announced on Oct. 15, 2010, that the Obama administration “strongly opposes” the initiative and “will vigorously enforce the (Controlled Substances Act) against those individuals and organizations that possess, manufacture or distribute marijuana for recreational use, even if such activities are permitted under state law.”

The drop in support for Prop. 19 after the Obama administration was pressured to visibly oppose marijuana legalization is more than coincidental. Political elites exert extensive influence over Americans’ policy opinions in general (see 1, 2, 3) and their referendum votes in particular (see 1, 2, 3). There is evidence that Democrats derailed popular support for Proposition 19, too.

For starters, Democratic voters in California were especially likely to change their support for Prop. 19 from September to October. While Republican opposition to Prop. 19 remained relatively stable, Democratic support declined by nine and seven percentage points in Field and PPIC Polls conducted during the final month of the campaign.

Moreover, the graph below shows that the drop in Prop. 19 support was particularly pronounced among the most politically interested Democrats in PPIC surveys. In September 2010, 75 percent of highly-interested Democrats supported the proposition compared with just 60 percent in October. Meanwhile, support from Republicans and less informed Democrats remained rather constant.

Graph by Michael Tesler

These results are consistent with John Zaller’s account of public opinion, which suggests that politically interested Democrats changed their opinions about Prop. 19 because they were the ones most likely to receive and accept the message that high-profile Democratic politicians opposed legalizing marijuana in California.

The Obama administration has been less vociferous in its opposition to subsequent marijuana initiatives. Not surprisingly, then, the second figure shows that Democratic voters in Washington, Colorado, Alaska and Oregon were much more supportive of marijuana legalization than California Democrats were in 2010. The display, in fact, shows that Democratic voters were roughly 20 percentage points more supportive of marijuana legalization initiatives, on average, in 2012 and 2014 than they were of Prop. 19 in 2010.

All told, these results suggest that Democratic politicians’ strong opposition to Proposition 19 helped derail marijuana legalization in California. The fate of future marijuana legalization initiatives, therefore, could depend on whether or not high-profile state and national Democrats voice their opposition to these propositions to the same degree as they did against California’s Prop. 19 in 2010.

Voters in Oregon, Alaska and the District of Columbia voted to legalize marijuana in the 2014 midterm elections. They joined Colorado and Washington, which did so in 2012. So could other states follow suit in 2016? The Washington Post's Niraj Chokshi breaks down the possibilities. (Jorge Ribas/The Washington Post)