Last month, the District of Columbia Court of Appeals heard arguments in Halbig v. Sebelius, which asks whether the Affordable Care Act permits the federal government to pay health insurance premium tax credits for plans sold through the federally facilitated marketplaces. In a new blog post, Sara Rosenbaum of the George Washington University School of Public Health and Health Services explains the plaintiffs’ argument and outlines the profound implications if the challenges succeed, including the potential damage to the new insurance marketplaces and the loss of affordable coverage for millions of Americans.