How good a businessman is Donald Trump? Maybe the answer doesn’t matter, since barring death or impeachment he’ll be the most powerful man in the world until January 2021, or even 2025, come what may. Or maybe it does matter, in the sense that the only positive spin to be put on his otherwise ridiculous presidency is that the irrepressible cunning of the real-estate tycoon will eventually win through for the good of America — and thereby, we must hope, the good of the free world — against opponents who have smaller cojones and less dealmaking prowess than the Donald...