Though betting odds had a 20 percent chance that Donald Trump would use his brief prime-time Oval Office address to declare a national emergency at the Mexican-U.S. border, he did not. Instead, he dedicated his time to a hodge-podge of lurid descriptions of violence juxtaposed to a plea for humanitarian aid. In no way does that mean the issue is settled, and a national emergency declaration remains very much in the mix as one way to break the logjam, appeal to the Republican base, reopen the government, and, oh, trigger a legal crisis. Just Wednesday, Trump claimed an “absolute right”...