Cato has a study up by David Boaz and David Kirby that contains the most thorough analysis I've seen on libertarian voters, including estimates on how large of a voting block they are and how the block is potentially capable of swinging close elections. It is also pretty honest about some of the problems libertarians have in gaining political influence, especially their inability (or unwillingness) to organize. From the abstract:

Not all Americans can be classified as liberal or conservative. In particular, polls find that some 10 to 20 percent of voting-age Americans are libertarian, tending to agree with conservatives on economic issues and with liberals on personal freedom. The Gallup Governance Survey consistently finds about 20 percent of respondents giving libertarian answers to a two-question screen.

Our own data analysis is stricter. We find 9 to 13 percent libertarians in the Gallup surveys, 14 percent in the Pew Research Center Typology Survey, and 13 percent in the American National Election Studies, generally regarded as the best source of public opinion data.

For those on the trail of the elusive swing voter, it may be most notable that the libertarian vote shifted sharply in 2004. Libertarians preferred George W. Bush over Al Gore by 72 to 20 percent, but Bush's margin dropped in 2004 to 59-38 over John Kerry. Congressional voting showed a similar swing from 2002 to 2004. Libertarians apparently became disillusioned with Republican overspending, social intolerance, civil liberties infringements, and the floundering war in Iraq. If that trend continues into 2006 and 2008, Republicans will lose elections they would otherwise win.

The libertarian vote is in play. At some 13 percent of the electorate, it is sizable enough to swing elections. Pollsters, political strategists, candidates, and the media should take note of it.

Hat Tip: Hit and Run.

The trouble with the analysis comes when you take into account national security. I'm sure that in just about any quiz you gave me that was limited to economic and social issues, I'd come out as a libertarian because I favor a small government approach in both realms. However, given that I supported both the Iraq War and the Patriot Act, I don't think it's accurate to include me in the same voting block with those who oppose both those policies with fervor. I tend to think of the fight against terrorism and Islamic fundamentalism as an epic battle in history of Western Civilization, but many (if not most) self-described libertarians would say that this is blowing things completely out of proportion. I see the wiretapping program as a prudent measure to protect the nation against terrorist attacks, whereas libertarians who may agree with me on other issues see the wiretapping program as a gross violation of civil liberties.  

It would be one thing if national security were a fringe issue, but it is clearly going to be the dominant issue for the foreseeable future and one in which differences are irreconcilable. I think this has two ramifications for the libertarian voting block. 1) The 10-to-20 percent of Americans who may be libertarian on economic/social issues will continue to split into two groups when you take into account national security. 2) Libertarian votes are less "in play" than Boaz and Kirby believe. There is a segment of the libertarian block that is so vehemently antiwar, that they would never vote for the more hawkish candidate, regardless of that candidate's views on economic/social issues. Likewise, hawkish libertarians would not vote for the candidate who is perceived as being more dovish. How large a block of libertarian voters are there who would be willing to set aside disagreements on national security to vote for the candidate who is closest to them on economic/social issues? I'm not sure, but I would surmise that it's a lot less than 10-20 percent.

I think a huge test of this will be how a Rudy Giuliani presidential candidacy is greeted by libertarians, assuming he runs. As far as economic/social issues go, Giuliani is probably closer to libertarians than any potential candidate. However, he has supported President Bush in all of the major national security debates, including the Patriot Act. His record as a crime-fighting mayor was built, in part, on pushing the envelope on civil liberties. All of this would make him unacceptable to many libertarians, despite his record on tax cuts, government spending, and gay rights.   

Incidently, Boaz himself was quoted in the September issue of TAS as saying:

"Giuliani pioneered the use of the mid-day, televised 'perp walk' for white-collar defendants who posed no threat to the community, and many of whom were never even charged with a crime," says Cato Institute Executive Vice President David Boaz. "It was a brutal way to treat people who were, after all, innocent until proven guilty — a combination of demagoguery and prosecutorial abuse that does not recommend him for an office whose executive powers have been vastly enhanced under Bush."