RaceDemVotesGOPVotesLibVotes(L) %(D) - (R)Margin
IN-SenDonnelly1,268,407Mourdock1,126,832Horning146,4535.8%141,575-4,878
MT-SenTester234,465Rehberg215,701Cox31,2876.5%18,764-12,523
MT-GovBullock234,980Hill226,555Vandevender17,7293.7%8,425-9,304
AZ-01Kirkpatrick117,422Paton109,508Allen14,4506.0%7,914-6,536
AZ-09Sinema108,056Parker101,089Gammill14,3616.4%6,967-7,394
MA-06Tierney179,603Tisei175,953Fishman16,6684.5%3,650-13,018
MI-11Curson159,267Bentivolio151,740Tatar11,6113.6%7,527-4,084
NH-01Shea-Porter171,356Guinta158,482Kelly14,9684.3%12,874-2,094
UT-04Matheson108,275Love105,629Vein5,7032.6%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.