WASHINGTON — Millions of people who get private health coverage through the Affordable Care Act would be at risk of losing it under the replacement legislation proposed by House Republicans, analysts said Tuesday, with Americans in their 50s and 60s especially likely to find coverage unaffordable. Starting in 2020, the plan would do away with the current system of providing premium subsidies based on people’s income and the cost of insurance where they live. Instead, it would provide tax...