Veronique — I’m not sure I can agree with that. Committed libertarians of the Cato variety may not be fickle (Reason magazine has been admirably brutal against both Bush and Obama). But such very serious, committed, consistent libertarians are very rare in America (and really, really rare everywhere else). They don’t come close to constituting a major voting block. I respect folks who seriously believe in liberty-maximization in all spheres of life, but that is not a power-brokering constituency in American politics and never will be. Many left-leaning self-described “libertarians” are libertarian (libertine?) on social-issues but Naderites on economic issues. Many conservatives are libertarian on economic and federalism issues, but un-libertarian on all sorts of issues like gay marriage or drugs. Here’s how I put it in the magazine the last time this argument surfaced:

Perhaps sensing an opportunity here, professional libertarians are flexing their muscle. The Cato Institute put out a paper holding that some 15 percent of voters are libertarian and that, more important, they are the much-coveted “swing voters” who decide elections. And in a number of very close elections in November, many libertarians seemed almost giddy that they might have been responsible for the defeat of Republicans.
In its most basic form, the libertarian complaint should be familiar by now: From Terri Schiavo to diarrheic spending, the GOP has betrayed its commitment to limited government. So, the libertarians reason, why not “experiment” with the Democrats a bit? They expand government too, but at least they’re more liberty-loving when it comes to drugs, sex, abortion, etc.
The problem here is that “libertarian” is a shmoo-like word but libertarians are not shmoo-like people (shmoos being the magical creatures from Lil’ Abner who could take any form and be anything). Everyone likes to think he’s in favor of maximizing freedom. But in reality most folks want to maximize only the freedoms they like. I often ask self-described libertarians if they support government censorship of hardcore pornography on Saturday-morning broadcast television. If they say yes, then they aren’t really pure libertarians. If they say no, I congratulate them on their consistency and tell them why their political ambitions are doomed.
“Libertarian-leaning” people are often quite severe about which “freedoms” they want liberalized and which they don’t. Indeed, they’re often single-issue voters. Just ask the folks at Libertarians for Life. Meanwhile, some doctrinaire libertarians are fixated on legalizing drugs, others on gay marriage, and some, amazingly enough, on defending the moral legitimacy of the Confederacy. A bloc of centrist swing voters this ain’t. The point is that most of the talk about “libertarians” switching sides has been exactly that, talk.

You also say:

As long as politicians fail to defend our freedom consistently, it is likely that libertarian-leaning voters will likely fail to commit to either group — not because they are capricious, but because they believe that more freedom is the way to a happier world for all of us.

I’m okay with that. But “consistently” defending our freedoms is a pretty loaded concept because people disagree on what “our freedoms” are. That’s true of libertarians themselves. For instance, some are pro-life, some aren’t. So any freedom-defending politicians will turn off some libertarians.

You end your post saying:

In the end, I think that the libertarians’ biggest mistake might to keep believing that either party can give them what they want.

You may be right. And while I’m not a big fan of third parties, a serious Libertarian party would be the least objectionable — to me at least — because I think it would help pull both parties in a mostly healthy direction. But I am dubious it will ever happen.