NEW ORLEANS—Rescue workers set out in hundreds of boats and helicopters to reach people trapped by floodwaters and utility crews mobilized Monday after a furious Hurricane Ida swamped the Louisiana coast and shattered a large swath of the state’s electrical grid in the sweltering, late-summer heat. One of the most powerful hurricanes ever to hit the U.S. mainland weakened into a tropical storm overnight as it pushed inland over Mississippi with torrential rain and shrieking winds, its danger far from over. Ida was blamed for at least one death—someone hit by a falling tree outside Baton Rouge—but with many roads impassable and cellphone service knocked out in places, the full extent of its fury was still coming into focus. The hurricane “came in and did everything that was advertised, unfortunately,” Louisiana Gov. John Bel Edwards said. All of New Orleans lost power right around sunset Sunday as the hurricane blew …