Joe Biden has promised that no families with incomes under $400,000 will see tax increases if he is elected president. But that’s a promise he won’t be able to keep if he gets his way and Congress creates a government-run health insurance plan—a public option.
Mr. Biden and other supporters of the public option argue it would be a relatively modest change to the nation’s health-care system because, unlike single-payer proposals, it would add nothing to federal deficits. But once enrollees and health-care providers start applying…