Third, madness is always a diminishing asset. At some point, all the good- and bad-cop playacting, and the proper alchemy of restraint and irascibility, must at least occasionally be followed by not just action but meaningful action. Obama ruined his international reputation by not bombing Syria to save gassed children after he’d issued a red line. But he did not redeem his credibility when he precariously bombed Qaddafi out of Libya — given that he perverted a U.N. resolution rather than confirmed a prior ultimatum, and he seemed to whine about his wrong action rather than be willing to right it by sending forces to stanch the terrorist wound he had inflicted.

So far, Trump has emphasized his unpredictability by allowing a field general to drop a MOAB weapon in Afghanistan and by bombing a chemical-weapons depot in Syria. But after his military braggadocio and his wild threats to redefine trade and build a wall, Trump will either have to put on a muzzle or follow through on his ultimata. Ranting madly about “making Mexico pay” for the wall will become an embarrassment — unless he quietly slaps a federal transfer tax on the $25 billion in remittances sent annually to Mexico, the vast majority of that sum likely wired by illegal aliens, who in some cases rely on American federal and state entitlements to subsidize their Mexican largesse.