The threat to do away with Obamacare is once again on the rise nearly 10 years after it was passed, as a major challenge to the health care law got a sympathetic-sounding hearing in a federal appeals court this week. If the case does ultimately reach the Supreme Court, and five justices agree to strike down the Affordable Care Act, experts say it would upend the U.S. health care system and strip health insurance from an estimated 20 million people. Many millions more would lose crucial protections they might need in case of catastrophic medical issues ― including coverage for...