Donald Trump is a deceptively conventional US president of the 21st century. Elected to unpick his nation’s entanglements in the Middle East, he has served to deepen and extend them. What most separates him from his immediate predecessors is his lack of an alibi. George W Bush had terrorist atrocities to avenge, even if he avenged them with a fiasco or two. As for Barack Obama, the Arab spring dawned and then darkened over the course of his tenure. It required an answer.
No external shocks of comparable size have forced Mr Trump’s hand. What has brought the US to its present showdown is, as well as Iranian goading, the paradox of his own worldview.
The president sincerely aspires to a lighter global workload for the US. But his very nationalism — his American amour propre — makes him amazingly easy to provoke into conflict. This glitch is not in the temperament of one man, but in the whole idea of America First, of nativism everywhere. It can have its chest-beating sense of honour or it can have its dream of a quiet life in a world of sovereign states minding their affairs. Having both seems fantastic, as the first will tend to compromise the second.