He sided with Republican plaintiffs in 20 states who argued that the entire ACA was rendered invalid when Congress zeroed out the financial penalties tied to the individual mandate.
The surprise decision Friday already has both sides of the debate posturing, with Democrats claiming the ruling is but a hiccup and Republicans suggesting this could be their chance, at last, to abolish the law - which remains largely in place despite President Trump's past claims to the contrary. If the decision is upheld, it could significantly disrupt the US health care system.
WellCare Health Plans and Anthem Inc declined 4.7 percent and 2.1 percent, respectively.
"If this bad ruling is upheld in the higher courts, it will be a disaster for tens of millions of American families, especially for people with pre-existing conditions", Schumer said in a statement.
"This is a backward, poorly-reasoned decision, but it does not change the fact that the Affordable Care Act is still the law of the land", said Democratic Maine Attorney General, and Governor-elect, Janet Mills.
"Regardless, the ACA will remain in effect for 2019, and we are optimistic that it will remain in effect thereafter". Much of the focus by the public after the decision has been on the 10 million people who buy insurance through the ACA marketplaces and the 12 million who are covered through their states' Medicaid expansion.
The challenge to the ACA brought by Republican attorneys general is aimed at eliminating protections for pre-existing conditions, Kodjak says.
For the next several weeks, then, health care and health insurance will be at the top of America's legal, legislative and political agendas.
The O'Connor ruling underscored the high political stakes involved in the divide over healthcare, especially for Trump and his fellow Republicans ahead of the 2020 presidential election.
Republican state officials, led by the attorney general of Texas, filed a lawsuit previous year arguing that getting rid of the penalty rendered the mandate unconstitutional. "This could all be an excellent buying opportunity depending on magnitude of moves and the next steps around another court entering a stay", Holz wrote.
However, the ruling has created uncertainty about the future of the ACA, even as many legal experts question O'Connor's reasoning and predict the ruling will get tossed out upon appeal. The ruling was opposed by healthcare groups and, if upheld, threatens to throw insurance markets into chaos and strip coverage from tens of millions of Americans.
He concluded the individual mandate "can no longer be fairly read as an exercise of Congress's Tax Power and is still impermissible under the Interstate Commerce Clause - meaning the Individual Mandate is unconstitutional", adding that the mandate is inseparable from the rest of the law.
The five justices who upheld the health law in 2012 in the first major case - Chief Justice John Roberts and the court's four liberals - are all still serving.
"This ruling is not going to affect people who are now enrolled who're in Obamacare policies or the policies for 2019", Collins said. While U.S. District Court Judge Reed O'Connor's 55-page opinion overturns the entirety of the law on a national basis, his ruling does not include any sort of injunction that would immediately cause employers to alter their practices with respect to benefit administration.
"It affects nearly everyone in America", said Tim Jost, a specialist in health law and a professor emeritus at Washington and Lee University. Those gains have translated to better health and productivity for hard-working people who once could not afford the high cost of coverage.
Former President Obama also weighed in on the issue, according to Fox News, reiterating to potential Obamacare enrollees that the law has not been struck down for good, and that he believes the Affordable Care Act will survive the appeals process.