Plummeting temperatures were expected to bring the coldest Christmas Eve on record, and energy systems across the country were strained by rising demand for heat and storm-related damage to transmission lines.In Erie County, in upstate New York, about 500 motorists were stranded in their vehicles on Friday night into Saturday morning, with the National Guard called in to help with rescues, Erie County Executive Mark Poloncarz told media.Two motorists were killed, and numerous others injured, in a 50-vehicle pileup that shut down the Ohio Turnpike in both directions during a blizzard near Toledo, forcing an evacuation of stranded motorists by bus to keep them from freezing, officials said.Three deaths were reported in Kentucky, where Governor Andy Beshear, on Saturday, warned residents, "Stay home, stay safe, stay alive."The challenge was compounded by an influx of migrants crossing the U.S. southern border by the thousands in recent weeks."