The Democrats’ nightmare scenario goes like this. Their coalition goes on fracturing, and finally splinters. At the next set of elections — Presidential and Congressional — an embittered, resentful left stays at home. That means young people and minorities, who don’t turn out. Meanwhile, some portion of the vast majority of American whites go back to their long-standing pattern — they vote Republican again, as they and their parents and grandparents always have. The right wins easily, and — hey presto — Trump’s back in office.