Measured purely in the currency of continuing U.S. influence in the region, Soleimani’s killing must be reckoned a failure. Sympathy has swung away from Washington and toward Tehran.

But what if Trump is serious and no longer cares about U.S. influence in the Middle East? What if he calculates that, as the U.S. becomes the world’s largest oil producer, the strategic case for an American presence in the region has become obsolete? What if he is sincere in his desire to pull the troops out — in good order, to be sure, but as swiftly as practically possible? What if he simply wants to make clear, as he departs, that any actions directed against the U.S. will be met by a terrible and disproportionate reaction?

If that is his goal, then surely he has succeeded. He has always made it clear that he regards the maintenance of overseas garrisons as an unnecessary drain on the treasury. His task, therefore, is to wind them down without encouraging every anti-American militant to rush whooping and screaming into the newly vacated territory. How best to achieve that objective? By making it clear that there will be a personal cost to the paramilitary leaders and militia commanders involved. Maybe it’s not such a bad approach.