Libertarians provided the margin for Democrats in at least nine elections

Race	Dem	Votes	GOP	Votes	Lib	Votes	(L) %	(D) - (R)	Margin
IN-Sen	Donnelly	1,268,407	Mourdock	1,126,832	Horning	146,453	5.8%	141,575	-4,878
MT-Sen	Tester	234,465	Rehberg	215,701	Cox	31,287	6.5%	18,764	-12,523
MT-Gov	Bullock	234,980	Hill	226,555	Vandevender	17,729	3.7%	8,425	-9,304
AZ-01	Kirkpatrick	117,422	Paton	109,508	Allen	14,450	6.0%	7,914	-6,536
AZ-09	Sinema	108,056	Parker	101,089	Gammill	14,361	6.4%	6,967	-7,394
MA-06	Tierney	179,603	Tisei	175,953	Fishman	16,668	4.5%	3,650	-13,018
MI-11	Curson	159,267	Bentivolio	151,740	Tatar	11,611	3.6%	7,527	-4,084
NH-01	Shea-Porter	171,356	Guinta	158,482	Kelly	14,968	4.3%	12,874	-2,094
UT-04	Matheson	108,275	Love	105,629	Vein	5,703	2.6%	2,646	-3,057

As we've perused last week's election returns, we'd noticed a number of races where Libertarian candidates appear to have played spoiler for Republicans'certainly, more than we're accustomed to. While we haven't run a comparison with prior cycles, we've identified no fewer than nine contests in 2012 where the Libertarian received more votes than the difference between the Democratic and Republican candidates. What's more, none of these involved the typical 1 or maybe 2 percent you ordinarily expect a Lib to garner: Looking at the three-way vote, all but one were over 3 percent, and three took 6 percent or more, with a high of 6.5 percent in the Montana Senate race. These definitely seem like unusually high figures.

So what's going on here? I wouldn't want to speculate too much based on this limited data set. But I could easily believe that a growing proportion of conservative-leaning voters are too disgusted with the GOP to pull the Republican lever, but who won't vote for Democrats either, are choosing a third option and going Libertarian instead. This thesis dovetails with something else we saw this year: independents generally leaning more rightward simply because at least some former Republicans are now refusing to identify with their old party. It's not much of a stretch to imagine that some folks like that don't want to vote for their old party either.

The chart above summarizes our findings, based on preliminary data from the AP, with a big hat-tip to my colleague Jed Lewison. (Note that MI-11 refers to the unexpired term for ex-Rep. Thad McCotter's seat, not the full-two year term that starts in January.) It's too facile to say that without the Lib, every Democrat would have lost. But some very likely would have, so it's reasonable to conclude that the Libertarian Party gifted quite a few seats to Team Blue this year. Thanks, friends!

2:51 PM PT: Incidentally, here's a list of other races where a third party also played a possible role in the opposite direction. The party or parties taking more votes than the difference between the first- and second-place finishers are listed after each race. First up, Republican wins:

AZ-Sen: Libertarian
NV-Sen: "None of the above" and Independent American Party
IN-Gov: Libertarian
CO-06: Libertarian and an independent
IL-13: An independent
IN-02: Libertarian
MI-01: Libertarian and Green

And Democratic wins:

MI-11: U.S. Taxpayers (in addition to Libertarian in chart above)
NY-24: Green

It's hard to imagine the Libertarians helping Republicans in IN-Gov, CO-06, IN-02, and MI-01, just like it's hard to imagine the Green Party helping Democrats in NY-24. However, it's not inconceivable that the Green hurt Dems in MI-01, though that may have been balanced out by the Lib (who got more votes). Something similar may have happened in CO-06 as well. IL-13 is harder to read, and Nevada's unique "none of the above" option is a real scrambler, though the IAP is decidedly right-wing. So is the U.S. Taxpayers party in MI-11, but as we noted, there was also a Libertarian there as well.

Fri Nov 16, 2012 at 10:32 AM PT: Matt Welch of Reason, sort of the house organ of the Libertarian movement, makes a good point: For Andrew Horning in IN-Sen to have been a spoiler in the true sense of the word, 97% of the votes that went his way would have had to go Republican instead. That's not very likely. So here are all nine races sorted by the vote percentage taken by the Lib that would have needed to go to the GOP candidate to change the outcome:

MA-06: 22%
UT-04: 46%
MT-Gov: 48%
AZ-09: 49%
AZ-01: 55%
MT-Sen: 60%
MI-11: 65%
NH-01: 86%
IN-Sen: 97%