What is the significance of Rand Paul to this discussion?

Rand Paul is clearly the most significant libertarian-leaning American political figure in a long time. There are a couple of issues I disagree with him on, but when you look at issues that cut across left-right boundaries, like his interest in reduced spending, less regulation, reining in our adventurous foreign policy, protecting America's rights against surveillance -- that's a combination of issues that libertarians have waited a long time to find together in one candidate. I think he can have a lot of appeal. A lot of libertarians, including those who came out of the Ron Paul movement but also others, are very interested in seeing how far his political ambitions might take him.

How does libertarianism figure into the war of ideas that's going on in the Republican Party? Is the GOP poised to embrace libertarianism?

I think they're poised to debate it. Rand Paul is going to be in the middle of the people debating the future of the Republican Party. Rand Paul has said he doesn't call himself a libertarian; he calls himself a libertarian Republican, small L-capital R, and he does sometimes say that the party needs to move in a more libertarian direction to broaden its appeal to young people and independent voters.

One of the things Ron Paul's campaign showed was that a lot of young people who were not Republicans were interested in these ideas. But [as a Republican politician] you either have to get those people into Republican primaries or you have to get the nomination for that to do you any good.

Rand Paul's supporters believe as soon as he starts to look like a contender, the establishment is going to see him as a threat and try to destroy him.

There are all sorts of Washington establishments who are going to want to take down Rand Paul. The spending establishment is certainly not going to like what he's talking about. The Republican political establishment doesn't particularly want to change. And certainly the national security establishment is extremely eager not to debate our policy of global interventionism. They have always sought to rule out of bounds any challenge to it.

They tried it in the Republican primary in Kentucky [in 2010]. The neocons organized one of their emergency committees to stop Rand Paul in the primary. I think they will continue to do that.

And yet some libertarians have started to criticize Rand Paul for going squishy as he tries to appeal more to the GOP mainstream.

If you want a pure libertarian to run for president, you've got the Libertarian Party. If you think the Libertarian Party's candidates aren't pure enough, you can write in Murray Rothbard. When we talk about a U.S. senator running for president, you are talking about the real world of politics. Nobody is going to be a doctrinaire Ayn Rand libertarian. Rand Paul has rounder edges than his father. He has a number of other advantages over his father: He's not 77 years old; he's a not a House member, he's a senator; and he has rounder edges in the way he presents libertarian ideas. There may even be issues on which they actually disagree, though I'm not sure I can think of one.