hot button

American Heritage® Dictionary of the English Language, Fourth Edition

1. n. Slang Something that elicits a strong emotional response or reaction: an issue that became a hot button among younger voters.

Wiktionary

1. n. idiomatic a central issue, concern or characteristic, especially one that motivates people to make a choice
2. n. idiomatic, marketing the principal desire that a salesman needs to "hit" in order to make a sale