Emmanuel Macron says it is “crazy” to think that Europe might use its most powerful economic weapon for the first time against, of all countries, America. But as Donald Trump doubles down on his threats to take Greenland, European leaders are weighing their retaliatory options. Their countries are well-positioned to weather the tariffs Mr Trump has promised. In a bigger economic war, though, all bets are off.

America’s president operates by instinct rather than ideology, frustrating those trying to make sense of his foreign policy. But his flexibility belies the fact that within the MAGA movement there are coherent—and competing—ideologies about how America should exercise power in the world. It is not yet clear which faction will prevail.