Complex sentence: The metaphor comes from the high-voltage third rail in some electric railway systems.Steping on this usually results in electrocution, and the use of the term in politics relates to the risk of "political death" that a politician would face by tackling certain issues.
Split into simpler sentences: The metaphor comes from the high-voltage third rail in some electric railway systems. Stepping on this usually results in electrocution, and the use of the term in politics relates to the risk of "political death" that a politician would face by tackling certain issues.