According to standard theory, we have Democrats on the left and Republicans on the right. In the primary phase of a campaign, the further extremes of the parties get some attention, as politicians of each party court the more extremist wings of their constituencies. Then, in the general election, the parties’ chosen candidates “court the center,” where the “swing voters” are.

The trouble with this? One important set of voters gets left out.

David Boaz and David Kirby, in a study prepared for the Cato Institute, note that 10 to 20 percent of the voting-age population does not fit on the standard left-right spectrum. These are the libertarians, who favor a general hands-off approach to the economy (like Republicans say they do) and a general hands-off approach to private and social life (like Democrats sometimes pretend to).

Though libertarians have a political party with their very name on it, only a few libertarians vote for it. Most are, in fact, swing voters.

In 2000, libertarians swung very strongly against Al Gore. In 2004, they shifted noticeably away from Bush. And libertarians sure didn’t seem to swing to Republicans this year.

But what will they do two years from now? Republicans have betrayed their more libertarian positions, and Democrats, well, they haven’t even gotten close to the ballpark.

In 2008, will the libertarian swing vote be courted by either major party? You’d think they would be, since, without them, politicians might not get elected.

This is Common Sense. I’m Paul Jacob.