The case that will be the biggest threat to ObamaCare is the case of Halbig v. Sebelius (it has now been renamed Halbig v. Burwell, after Sebelius was pressured to resign as HHS secretary).
It was argued before a three-judge panel of the U.S. Court of Appeals for the D.C. Circuit Court in March.
It attacks the central nervous system of ObamaCare — the government exchanges that were set up to subsidize health insurance for low-income consumers.
If the Supreme Court ultimately finds that the Obama administration violated the law in doling out those subsidies, it could force a wholesale revision of ObamaCare.