third rail

US /ˌθɜːrd ˈreɪl/
UK /ˌθɜːrd ˈreɪl/
"third rail" picture
1.

terceiro trilho, assunto delicado

a political issue that is so controversial that any politician who dares to broach the topic will suffer a backlash from voters

:
Healthcare reform has become a third rail issue in American politics.
A reforma da saúde tornou-se uma questão de terceiro trilho na política americana.
No politician wants to touch the third rail of social security.
Nenhum político quer tocar no terceiro trilho da segurança social.