The ruling by a federal judge in Texas striking down the Affordable Care Act has injected a powerful wave of uncertainty about recent changes woven into the U.S. health care system that touch nearly all Americans and the industry that makes up one-sixth of the economy. The opinion, if upheld on appeal, would upend the health insurance industry, the way doctors and hospitals function and the ability of millions of Americans to access treatments they need to combat serious diseases. Parts of the law that would need to be unwound include no-charge preventive services for older Americans on Medicare, allowing parents to keep children on their plans through age 26, a variety of efforts to rein in prescription drug costs and even requirements that some restaurants post calorie counts “It affects almost everyone in America,” said Tim Jost, a specialist in health law and a professor emeritus at Washington and Lee University. The court decision also sets up an awkward juggling act for the Republican Party, balancing President Donald Trump’s gleeful tweets over the court’s decision against a perception that the GOP is threatening insurance that covers nearly 20 million Americans through new private health plans and an expansion of Medicaid — a perception that Democrats successfully employed in last month’s elections that gave them control of the House. While the ruling by U.S.