President Donald Trump’s new executive order instructing federal agencies to grant relief to constituencies affected by the Affordable Care Act has begun to reverberate throughout the nation’s health-care system, injecting further uncertainty into an already unsettled insurance landscape. The political signal of the order, which Trump signed Friday just hours after being sworn into office, was clear: Even before the Republican-led Congress acts to repeal the 2010 law, the new administration will move swiftly to unwind as many elements as it can on its own – elements that have changed how 20 million Americans get health coverage and what benefits insurers must offer some of their customers.