lightning rod

American Heritage® Dictionary of the English Language, Fourth Edition

1. n. A grounded metal rod placed high on a structure to prevent damage by conducting lightning to the ground.
2. n. One that attracts and absorbs powerful, typically negative feelings and reactions, thereby diverting interest from other issues: "[His] business dealings have become a lightning rod for criticism” ( Walter Shapiro).

Century Dictionary and Cyclopedia

1. n. A pointed, insulated metallic rod erected to protect a building or a vessel from lightning; a lightning-conductor. ; Lightning-rods are attached to buildings and other structures for two purposes: to prevent as far as possible sudden discharges of electricity from clouds to earth through or in the neighborhood of the building

Wiktionary

1. n. A metallic conductor that is attached to a high point of a building and leads to the ground and protects the building from damage by lightning
2. n. figuratively A person or thing that is a target for negative reactions and distracts criticism from another target.

GNU Webster's 1913

1. n. a metallic rod set up on a building, or on the mast of a vessel, and connected with the earth or water below, for the purpose of protecting the building or vessel from lightning.

WordNet 3.0

1. n. a metallic conductor that is attached to a high point and leads to the ground; protects the building from destruction by lightning
2. n. someone who is a frequent target of negative reactions and serves to distract attention from another