The following is a guest post from Paul-Henri Gurian, associate professor in the Department of Political Science at the University of Georgia.
University of Georgia Political Science Professors Paul-Henri Gurian and Audrey Haynes, together with Drs. Nathan Burroughs, Lonna Atkeson and Damon Cann, have published a study that measures the impact of national party division on presidential elections. Their results are relevant to the current party divisions, especially within the Republican party.
History shows that when one party is divided and the other party is united, the divided party almost always loses the presidential election. Consider, for example, the elections from 1964 through 1984; in each case the divided party lost. The study measures party division during the primaries and indicates how much the more divided party loses in the general election.
The study shows that both national party division and divisive state primaries have significant influence on general election outcomes. But national party division has a greater and more widespread impact on the national results. A divisive state primary can have a small negative impact on that one state, but national party division can have large negative impact on the national vote. A divisive state primary rarely leads to more than a 1-2% decrease in the general election in that state. For example, Hillary Clinton received 71% of the Democratic vote in the Georgia primary while Donald Trump received 39% of the Republican vote. If nominated, Trump would lose almost 1% in the state of Georgia in the general election.
In comparison, national party division often leads to decreases of more than 3% nation-wide. For example, as of March 12, Trump has received 36.1% of the total national Republican primary vote while Clinton has received 60.0% of the Democratic vote. If these proportions remain steady for the remainder of the nomination campaign (and if these two candidates win the nominations), then Trump would lose 5.7% of the vote in the general election (compared to what he would otherwise be expected to receive). In a close election (such as 2000, 2004, 2012), 5-6% could change the outcome in terms of which party wins the presidency.
The results of this study provide analysts with a way to anticipate the impact of each primary and, more importantly, the impact of the total primary vote on the general election results. Subtracting the percent of the Republican nominee’s total popular vote from that of the Democratic nominee and multiplying that by 0.237 indicates how much the Republican nominee is likely to lose in the November election (compared to what would otherwise be expected). The 5.7% figure calculated through March 12 can be updated as additional states hold their primaries. (The same can be done for individual state primaries by multiplying by 0.026.)
The full study, “National Party Division and Divisive State Primaries in U.S. Presidential Elections, 1948-2012,” published by Political Behavior, is available online now (http://link.springer.com/article/10.1007/s11109-016-9332-1). Contact Dr. Gurian at PHGurian@uga.edu for further information, questions or clarification.