Today, the Supreme Court will hear arguments in King v. Burwell, a case that threatens to yank the tax credit away from Donald and millions of other people like him. Under the Affordable Care Act, otherwise known as Obamacare, the states were invited to create exchanges, or online marketplaces, where uninsured individuals must buy insurance plans. In the states that opted not to create one—either for logistical reasons or out of political opposition to the law—consumers were told to use an exchange created by the federal government through Healthcare.gov. Florida is one of these states.

The law also stipulates that people below a certain income threshold, about $47,000 a year for an individual, get tax credits to help offset the cost of their insurance plans. King v. Burwell hinges on, essentially, four words: In the section of the law that discusses these tax credits, the text refers to an exchange “established by the state.” That would imply, the plaintiffs' lawyers will argue, that the tax credits should not extend to the 34 states that operate on the federal exchange. The Internal Revenue Service, they say, is illegally offering those tax credits to people in those states.

States That Risk Losing Subsidies After King v. Burwell

David King, the lead plaintiff, is a Virginia Vietnam vet who hates the very thought of a law that requires him to buy insurance. Mother Jones and The Wall Street Journal have raised questions about whether King is actually affected by the law, since veterans are usually eligible for free healthcare anyway. But others say he and the other plaintiffs do have the proper legal standing.

“When you look at the rules, just because you may have had military service at some point in time, he might not actually in the full sense qualify for eligibility by the VA,” Thomas Miller, a resident fellow at the American Enterprise Institute, told me.

If the Court goes for King, Obamacare as we know it might end. In a recent analysis, the Urban Institute noted that more than 9 million people currently live in states that use a federal exchange and receive subsidies. It estimates that they would lose about $3,000 in tax credits each, and 8 million of those people would become uninsured. Because so many people would pull out of these insurance markets, the cost of insurance premiums in those states would skyrocket by 35 percent, the think tank estimated. As the cost of coverage rises, fewer people would want to enroll. The goal of Obamacare—to cover all Americans—would be hobbled.

Most people who will be affected by this case do not realize they will be. According to a January poll by the Kaiser Family Foundation, 56 percent of Americans say they have heard “nothing at all” about King v. Burwell. In fact, most people do not know what kind of exchange their state uses, which suggests that these people might be blindsided by the ruling.