Why is Social Security considered a 'third rail' in American politics?

Social Security is considered a 'third rail' in American politics because more than 70 million Americans rely on it for their financial security. As Rachel Maddow emphasizes, people know it's not a scam but an essential program that supports tens of millions of citizens. The term 'third rail' refers to how politically dangerous it is to propose cutting or eliminating Social Security. Politicians who characterize it as a 'scam' risk significant backlash from voters who depend on these benefits, which is why Maddow anticipates that those promoting such negative narratives will face serious political consequences.