Did Gary Johnson and Jill Stein Cost Hillary Clinton the Presidency? A Counterfactual Analysis of Minor Party Voting in the 2016 US Presidential Election

Hillary Clinton won the national popular vote for president in 2016, but lost to Donald Trump in the Electoral College. Trump’s margin of victory in several decisive battleground states was smaller than the combined vote for the two leading minor party candidates: Gary Johnson, of the Libertarian Party, and Jill Stein, of the Green Party. The perception that Johnson and Stein 'stole' the 2016 presidential election from Clinton is widespread, and potentially consequential for future minor party candidacies, but it has not yet been rigorously tested. In this article, we extend Lacy and Burden’s (1999) analysis of minor party voting in the 1992 election, by using data from the 2016 Cooperative Congressional Election Study to estimate a multinomial probit model of voting behavior - including outcomes for vote choice and abstention - and calculate the predicted probabilities that Johnson and Stein voters would have voted for another candidate or abstained from voting, had one or both of these candidates been excluded from the ballot. We then reallocate Johnson’s and Stein’s votes accordingly, to estimate Clinton’s and Trump’s counterfactual vote shares nationally and within key battleground states. Our analysis indicates that Johnson and Stein did not deprive Clinton of an Electoral College majority, nor Trump the legitimacy of winning the national popular vote. We estimate that most Johnson and Stein voters would have abstained from voting if denied the choice to vote for their preferred candidate, and that most of Johnson’s remaining voters would have supported Trump