The 12-point swing is one of the largest shifts in support toward Democrats that the Reuters/Ipsos poll has measured over the past two years. If that trend continues, Republicans will struggle to keep control of the House of Representatives, and possibly the Senate, in the November elections, potentially dooming President Donald Trump’s legislative agenda. “The real core for the Republicans is white, older white, and if they’re losing ground there, they’re going to have a tsunami,” said Larry Sabato, a UVA political scientist who closely tracks political races. “If that continues to November, ...