14 March 2018 — 2035 mst
Did a Libertarian help Lamb defeat Saccone in PA-18?
What impact will third party candidates have in Montana?
That’s possible, but probably not provable. With approximately 500 ballots (military and provisional) left to be counted, Democrat Conor Lamb is leading Republican Rick Saccone by 627 votes in the special election in Pennsylvania’s 18th congressional district, an open seat. Libertarian Drew Miller has 1,379 votes.
The conventional wisdom is that third party candidates take votes away from the major party candidate closest to them on the ideological continuum. Green Party candidates hurt Democrats, Libertarians hurt Republicans. The CW has some merit, but a voter who is inclined to vote for a third party has several choices when his preferred third party candidate is not on the ballot: (a) voting for the closest ideological match on the ballot, (b) voting for a third party or independent candidate that is on the ballot, (c) casting a write-in vote, or (d) not voting.
The political science literature that I’ve consulted suggests that approximately half of the voters will choose option A. Therefore, by that rough — very rough— rule of thumb, in PA-18, Miller may have diverted approximately 690 votes from Saccone, enough to tip the election to Lamb. That scenario is plausible, but not provable. It’s also plausible that many of Miller’s voters were cast by Republicans who could not bring themselves to vote for Saccone, but could neither vote for Lamb nor not vote.
Greens and Libertarians in Montana
How to evaluate the impact of third party candidates on major party candidates has relevance for Montana, where both Greens and Libertarians will be on the ballot for the U.S. House and Senate. Libertarian will be on the ballot in 20 Montana legislative races, Greens in three.
The Green candidate may not have much impact on the federal races because Democrats want to win and are not likely to throw away their votes for the fleeting satisfaction of voting for a putatively more liberal candidate.
In 2012, Jon Tester defeated Dennis Rehberg 236,123 to 218,051, a margin of 18,072 votes. Libertarian Dan Cox received 31,892 votes (6.6 percent). The one-half rule of thumb suggests Cox may have depressed Rehberg’s total by 15,946 votes, not enough to have changed the election’s outcome. Whether 2018 U.S. Senate Libertarian Rick Breckenridge will do as well as Cox is open to question, but he could receive votes from Republicans unable to vote for Matt Rosendale, the likely GOP candidate, and unwilling to not vote or to vote for Tester.
Greens won’t make a difference in House Districts 15 and 85, but the Green candidate in Senate District 49 (Missoula) may be a problem for incumbent Democrat Diane Sands, who won 3,933 to 3,902 (I think that margin was narrowed to 14 votes after a recount).
I’m still reviewing the potential impact of Libertarians on legislative elections.