Beside the olive display at Zabar’s, that iconic hub of lox and neurosis on the Upper West Side of Manhattan, Linda Donohue was trying to talk herself down. Surely the polls she tracked anxiously were not to be trusted, she said. Surely Donald J. Trump, the man with the garish golden tower across town, would not be allowed to reach the White House. “We have to have more faith in the American public,” said Ms. Donohue, 61, a longtime New Yorker now living in Seattle. A man behind her could not suppress a loud snort. Then Cathi Anderson, who was...