The third rail of a nation's politics is a metaphor for any issue so controversial that it is "charged" and "untouchable" to the extent that any politician or public official who dares to broach the subject will invariably suffer politically. The metaphor comes from the high-voltage third rail in some electric railway systems. Touching a third rail can result in electrocution, so usage of the metaphor in political situations relates to the risk of "political suicide" that a person would face by raising certain taboo subjects or having points of view that are either censored, shunned or considered highly controversial or offensive to advocate or even mention. It is most commonly used in North America. Though commonly attributed to Tip O'Neill, Speaker of the United States House of Representatives from 1977 to 1987, it seems to have been coined by O'Neill aide Kirk O'Donnell in 1982 in reference to Social Security.

American examples of usage

A wide range of issues might be claimed detrimental to politicians tackling them, but those below have all been explicitly described using the "third rail" metaphor:

Outside the U.S.

Argentina

Australia

Canada

Denmark

Germany

India

Republic of Ireland

United Kingdom

China

Singapore

The term OB marker ("out of bounds marker", a golf term) is widely used in Singapore for forbidden topics, such as:

Serbia