Politically there have been libertarian candidates for president, notably former Rep. Ron Paul (Rand Paul's father). Ron Paul's tallies were marginal in his first two presidential runs, as an independent in 1988 and in the Republican primaries in 2008. He fared better in the 2012 GOP primaries, starting strong, then fading because of a lack of funds.

There have been movements promoting these ideas. The most famous one is that founded by Ayn Rand, a novelist and propagator of what she called objectivism. Her novels stressed the importance of individualism and the Enlightenment. She was critical of religion as a belief system rendered irrational by philosophy, which superseded it.

Libertarianism is most simply defined as a basic hostility to the government and its institutions. A full-fledged libertarian wants few (if any) state-owned enterprises, no constraints on private enterprises by government regulations, extremely low taxes, total individual freedom in the social realm, primacy of privacy rights over governmental intrusion, and the reduction of armed forces and police to a minimum. Libertarians rule out any kind of government-backed social protection such as pensions and unemployment insurance. Much of this appeals to deep cultural roots in the United States. But the full program is so extensive that very few people have been ready to embrace it completely.

The combination of these two features has made it virtually impossible for third party candidates to win presidential elections or to be more than spoilers. Up till now, libertarians have largely run as third party candidates. Libertarianism has never been, therefore, an important force in affecting policy choices or electoral preferences. The seriousness of the attempts by Sen. Rand Paul to obtain the Republican nomination has changed all that.

However, the actual mechanics of the elections in different countries vary. The system used in the United States has been possibly the most constraining in maintaining this two-party pattern. This is the result of two features in the U.S. Constitution. The first is the exceptionally important role of the president, leading parties to put winning the presidential election as their first priority. The second is the curious system by which the president is chosen — by the Electoral College, in which, for 48 out of 50 states, the winner of the most popular votes takes all its electoral votes.

The general elections of most countries with parliamentary systems have largely functioned in the same way. They have had some regular alternation between two parties, one ostensibly left of center and one ostensibly right of center. In these systems, there has been little difference between the two main parties in terms of foreign policy and only a limited set of differences on internal politics, centering on issues of taxation and social welfare.

The previous two-party swing of compromise between two parties that are not all that different may not be able to survive the intrusion of libertarianism into the heart of U.S. politics.

So what is new? What is new is that Rand Paul won a seat in the U.S. Senate as a Republican in 2010. He won first the Republican primary and then the election largely as the result of fervent support from tea party Republicans who objected to his primary opponent as too establishment and too centrist in his orientation.

As soon as he became a senator, Paul began to play an important public role in asserting libertarian values and building an organizational base for his candidacy in 2016 (and thereafter). He has presented himself as less rigid in his interpretation of libertarianism than his father, seeking thereby to create a more substantial voter base. Nonetheless, his candidacy is shaking up the way U.S. politics has been working.

There are three sets of issues on which Rand Paul does not conform to the traditional Republican-Democratic discourse: the economy, social questions and foreign policy. On the economy, he has sought to go further in his anti-government position than the erstwhile mainstream Republicans. On taxes, on state expenditures and on the so-called deficit, he stands out as a tea party hawk. This meets considerable opposition from big business supporters of the Republican Party who generally feel his policies will make things worse, not better, for their interests. Still, on economic issues, he comes closest to being a traditional Republican.

On social issues, however, he is drawing very different lines of cleavage. He is generally supportive of the argument that the state does not belong in the bedroom and that the choices on how to govern one's life should remain with the individual. In addition, and not least, he is fiercely opposed to the role of the National Security Agency and other state structures in violating the privacy of U.S. residents. Recently, he took these causes to a major locus of left sentiment, the student body at the University of California at Berkeley. There he made a speech along these lines that was wildly applauded. One of his Republican critics said of this speech that there was hardly a Republican sentiment in it.

And then there is foreign policy. He has expressed serious reservations about the belief that the United States has a role (even a political role, a fortiori a military role) in promoting democracy in other countries. He goes perhaps not as far as his father, who recently said Russia's annexation of Crimea was not something on which the United States should be having a position. Here, too, the lines he draws politically are not conventional. His views bring together some far-right Republicans and the liberal wing of the Democratic Party.

The bottom line of all this is that the previous two-party swing of compromise between two parties that are not all that different may not be able to survive the intrusion of libertarianism into the heart of U.S. politics. Libertarians are now a somewhat unpredictable joker. They constitute a third force. And the result may be that third parties — not necessarily only the libertarians — may be able to turn a two-party system into a three-party system, even within the constraints of the U.S. Constitution.

We shall see after 2016.