Instead of debating how to expand Medicare coverage, politicians should focus on fixing the fatal financial flaws in the existing program that threaten to bankrupt the nation.

Medicare spent 3.6% of gross domestic product in 2016, more than six times the share it consumed in 1967, the first full year it was implemented. The forecasts I have analyzed show that the share of GDP will rise to at least 9% within 75 years—and that’s the good-news scenario. Other plausible forecasts show that Medicare could spend more than twice that.