It’s a strange campaign season, loaded with fantastical promises of government handouts for health care, college and even a guaranteed national income. But Sen. Elizabeth Warren ’s Social Security plan takes the cake. With trillion-dollar federal budget deficits and Social Security heading for bankruptcy, Ms. Warren proposes to give every current and future Social Security recipient an additional $2,400 a year. She plans to finance her proposal, which would cost more than $150 billion annually, with a 14.8% tax on high-income individuals. If Franklin D. Roosevelt were alive, he’d surely wonder why anyone calling herself a Democrat would want to...