In a 7-2 ruling penned by Justice Stephen Breyer, the United States has rejected a challenge to the Affordable Care Act, aka Obamacare, brought by 18 Republican states. You can read the opinion here. Justice Clarence Thomas concurred, while Justices Samuel Alito and Neil Gorsuch dissented.
What killed this challenge was the Court's conclusion that the challenging states lacked standing. It declined to rule on the merits of the challenge. "Neither the individual nor the state plaintiffs have shown that the injury they will suffer or have suffered is “fairly traceable” to the “allegedly unlawful conduct” of which they complain," noted Breyer.
In his dissent, Justice Alito grouses this "is the third installment in our epic Affordable Care Act trilogy, and it follows the same pattern as installments one and two. In all three episodes, with the Affordable Care Act facing a serious threat, the Court has pulled off an improbable rescue."
Interestingly, Trump appointees Brett Kavanaugh and Amy Coney Barrett sided with the majority.