The current conflict itself is largely a result of Mr. Trump’s renouncing the nuclear deal President Barack Obama achieved in 2015 along with Britain, France, China, Germany and Russia, and then reimposing crippling sanctions on Iran. And the targeted killing of General Suleimani was not only dubious in legal and moral terms, but also an act that may well backfire before long with some vicious retaliatory strike by Iran or one of its proxies.

The killing, moreover, served to further distance Washington from its European allies, none of which were notified in advance of a potentially incendiary action, and none of which endorsed it after the fact.

The subsequent decision by Germany, France and Britain to formally accuse Iran of breaking the 2015 deal by announcing it was no longer bound by its limitations, setting off a dispute mechanism, may not have been the show of solidarity that it seemed to be at first. While the Europeans were considering the action, the Trump administration had secretly threatened to impose a 25 percent tariff on their automobiles if they didn’t take the action, The Washington Post reported.

The killing had all the hallmarks of the Trump administration’s disjointed approach to foreign affairs. Assassination is illegal in international law and taboo American foreign policy, facts Mr. Trump’s national security team seemed to acknowledge when it initially issued inconsistent and unsubstantiated claims that General Suleimani was killed to prevent a big strike in which many Americans would have died. Mr. Trump ended the charade on Monday when he tweeted that “it doesn’t really matter” what the Iranian was up to. “Bad person, killed a lot of Americans, killed a lot of people. We killed him,” was the president’s typical sledgehammer response to dealing with the outside world.

That explanation pleased hawks who chafe at any restraint on the use of American muscle. “To put it simply,” as Senator Tom Cotton, the hawkish Republican from Arkansas, wrote in The Times, “the ayatollahs are once again afraid of the United States because of this bold action, which is forcing them to recalculate their odds.”