Divorce usually isn’t a good idea, and that’s especially true of a nearly 250-year-old continental nation. The notion of a national breakup has long simmered as a fringe argument, but it is increasingly popular in certain precincts of the political right and has gained at least some traction with partisans of both sides. A recent survey by the Center for Politics at the University of Virginia found that about 50 percent of Donald Trump voters and 40 percent of Joe Biden voters agreed to some extent with the proposition that the country should split up, with either red or blue...