Obamacare is back before the Supreme Court in a case that could gut the health care law and leave millions of Americans facing severe consequences. King v. Burwell, a lawsuit that originated in conservative and libertarian think tanks, alleges that a stray phrase in the Affordable Care Act -- “an exchange established by the state” -- means the federal government isn’t allowed to provide subsidies to the residents of states that refused to establish health insurance exchanges under the law. Only 13 states and the District of Columbia have their own exchanges.