If you want to understand the consequences of a potential ruling against Obamacare in the new Supreme Court challenge, King v. Burwell, this graphic from Vox's Joss Fong is the clearest summary.
The Supreme Court case centers on one big question: does the federal government have the legal authority to help Healthcare.gov enrollees pay for health insurance coverage?
If the answer is no, the subsidies go away — and health insurance gets more expensive. A lot more expensive. Without the subsidies, the average Obamacare enrollee's 2015 premiums would increase by 256 percent.
And that's just for 2015 — premium spikes would likely be bigger in 2016, when insurers have a chance to set new rates. After the initial premium hike, you can imagine that healthy people will simply drop their policies; why bother paying so much for a policy they barely use, after all? People with health issues — who use the coverage more — would be more likely to keep their plans. This would be a classic insurance death spiral: premiums go up and up as only the sick people stick around. That's why this decision matters so much for the Affordable Care Act, and whether the law continues to make insurance coverage accessible.