From Politico, signs that the libertarian moment (more about that here) proceeds apace:

Libertarians could be spoilers in key Senate races

Democratic hopes of maintaining a razor-thin Senate majority may hinge on an unexpected outside force: Libertarians. In the battlegrounds of Montana, Arizona and Missouri, polls show the Libertarian nominee poised to siphon a fraction of the vote — a small fraction, to be sure, but potentially enough to tip the outcome in a cliffhanger. And with the battle for the Senate shaping up to be a coin-flip proposition, no factor — not even fringe candidates with little more than a Libertarian label to propel their campaigns — is too insignificant to dismiss…. "Ralph Nader in reverse" was how Arizona GOP strategist Jason Rose characterized the 2012 dynamic. "When candidates bloody each other up, non-descript candidates can become safe harbors," he said….

Ralph Nader! Non-descript! Does that even make sense? Individual LP candidates may well be non-descript, but the party stands for some totally well-defined ideas and policies (as did Nader in 2000, when Al Gore lost the presidential race despite being part of a highly successful administration).

Let it be noted that no third-party candidate anywhere ever cost a major-party candidate an election. Have third-party candidates gotten vote totals that more than cover the spread between the Dem and the Rep? Of course.

But major-party candidates lose elections all on their own. If they cannot close the deal with voters—even with all the institutional advantages they possess—well, that's their problem. Don't blame others for your own failure to woo voters.

Indeed, the whole spoiler thing tends to falls apart when you look more closely. To wit, here's part of the discussion about the Senate race in the Show-Me State, where a lackluster and thoroughly undistinguished incumbent is facing a challenger whose basic grasp of biology suggests he'd be a first-question washout on Are You Smarter than a 5th Grader?:

Given the unpopularity of both M[Democratic incumbent Claire] Caskill and [GOP challenger Todd] Akin, [Libertarian Jonathan] Dine could see that support grow this year. An Oct. 3 poll by PPP found McCaskill up by 6 points, with Dine pulling 9 percent of the vote. About one-quarter of his support came from self-identified conservatives, his largest bloc of support.

More here.

When you're suggesting anything other than Todd Akin's big stupid yap and a voting record that includes most of the Bush era's greatest big government hits, plus Obama era highlights such as the National Defense Authorization Act, might cost him the election, you're shifting responsibility in precisely the way conservative Republicans cry about. Note that in Politico's telling, three-quarters of Dine's support comes from non-conservatives, so it's far from clear precisely why he can be the ultimate cause if and when Akin dogs it. How many of that remaining 75 percent is pulling voters who otherwise somehow "belong" to McCaskill? And if McCaskill can't secure re-election as a senator—over 80 percent of distinguished gentlemen and ladies manage the feat—that's her problem. (For more on Dine, a twice-convicted felon, read this enaging profile.)

In a related note, the latest iteration of the Reason-Rupe poll (conducted in early September) found that the 6 percent of voters who said they favor Libertarian presidential candidate Gary Johnson reduced support for both Barack Obama and Mitt Romney. Each major-party candidate came in three percentage points lower when Johnson was included in the mix. There's no question that traditionally, Libertarian voters were probably more likely to come from the Republican side of the electorate, especially if elections were based on economic issues. But given the prominence of war, immigration, trade, and lifestyle issues over the past dozen years—and the GOP's conservative lurch on all—it's likely that Libertarians really are increasingly equidistant from both parties.

In any case, I suspect that most big and small l libertarian-minded voters would be happy to vote for any major-party candidate who consistently fought to reduce the size, scope, and spending of government in a consistent and principled way. In fact, libertarian votes should be among the easiest to secure since there are virtually no outlying issues to core ideas. If Democrats and Republicans choose to toss those votes out the window, that's too bad for them (and the country).

More on this same type of Libertarian spoiler thing, in the New York Times, circa 2002.