The secretary may have prevailed this time, but, as reports of the internal debate surfaced, officials in Washington were left to wonder: At what cost? Foreign-policy veterans told me they were worried that Trump would finally tire of Mattis, as he has soured on so many other top advisers, though White House officials were at pains to deny any sense of a rift between the two. (“False,” the spokeswoman Sarah Huckabee Sanders said in an e-mail, when I asked about the Trump adviser’s sense that Trump had deferred to Mattis on the strike.)

Still, Syria is just one on a long list of issues, from Trump’s threat to withdraw from the Iran nuclear deal to his unilateral recognition of Jerusalem as Israel’s capital, exit from the global climate-change pact, and imposition of trade tariffs, on which Mattis has now been publicly identified as disagreeing with his loyalty-obsessed boss. “Either you conclude his influence is very high because of where Syria turned out,” one of the city’s national-security eminences, who has met with many of Trump’s officials in recent months, told me, “or it’s the beginning of the end.”