Beirut, Lebanon(CNN) It is perhaps the most brazen attack Iran has launched against the United States in four decades of simmering covert and overt conflict.

The timing. The target. The threats of heavy retaliation already "locked and loaded," as President Trump would have had it.

Yet Wednesday morning's missile strikes against al-Asad airbase and Erbil airport -- both of which play host to US troops -- were clearly not an act designed to kill the most Americans possible.

Iran will have known that the troops are normally asleep in the early hours of the morning. Choosing to attack then likely minimized the number of personnel roaming around the base who could be killed or injured.

It will also have known the US has a strong air defense system that would have been on high alert. Tehran should have a grasp of how well its missiles would fare against such technology.

The missile attacks don't make sense if Tehran's goal was to really hurt US troops in large numbers -- as some had been pledging to do.

They do make sense, however, as the execution of Supreme Leader Ali Khamenei's order to strike back openly, military-to-military, in response to the killing of Iranian commander Qasem Soleimani.

Khamenei's instruction was confusing when first reported, given that the US would be bound to prevail in a straightforward military conflict. Was the Supreme Leader ordering an empty show of force?

Wednesday's strikes sent a message that Iran would violate US red lines and engage in direct warfare, but they killed nobody.

The only thing wounded might be Iranian military pride that a moment they had so heavily trumpeted drew no blood from their adversary.

Three possible explanations

The dust is still settling, and even at the best of times Iran's motivations can be opaque, but there are three possible explanations for the action.

First, that Khamenei, Iran's octogenarian Supreme Leader, is out of touch with what his military can achieve and overestimated the effectiveness of the strikes, which then failed.

Such a miscalculation would be surprising, given his reported involvement in and knowledge of Iranian military affairs.

Second, that moderation won out, and this largely empty signal -- hitting military targets in the dead of night with a small number of missiles -- provides the off-ramp both sides might ultimately have been looking for.

This would be logical, given that neither Tehran nor Washington has much to gain from a prolonged fight.

Third, it might be a bid by Iran to lull the US into a false sense of security -- that Iran is militarily weak and has done its worst -- while an asymmetrical and nastier response is plotted.

That would require a lot of strategic acumen from a government split between hardline and moderate wings, and would mean Tehran was relatively certain no Americans would be hurt in this missile attack.

It is possible Iran allowed a warning to be passed to the US. The Iraqi Prime Minister's office said it was given verbal notification from Tehran just before the attack happened. It's hard to see how the US would not learn of that somehow.

Risk of further action

If the attacks in Iraq are indeed the full scope of Iran's response, they carry another risk: That the Trump administration thinks its ramshackle performance over the past week has paid off, and Iran has been vanquished.

This would risk further irrational action from Washington, perhaps not just against Iran but also other enemies. It would also make Iran look weak, which might embolden Tehran's other regional adversaries.

Much will hinge on Donald Trump's mood as he awakes. On what Fox News says. And on whether he feels slighted by Iran's rhetoric.

Iran's foreign minister, Javad Zarif, has sent the clear message that Iran does not want war. It is notable that his moderate English-speaking voice has been heard clearly throughout this volatile morning, at a time when moderation might be considered to have taken a back seat.

Trump may just take that off-ramp. Tehran and Washington have one thing in common: Their lack of appetite for a prolonged, open conflict with the other. Iran has a weak economy and internal dissent. Trump wants re-election and not another episode of "sand and death."

Iran has made its loud, public and fiery retort to the startlingly open killing of the country's top commander. Its allies can read into this courage, and even choose to believe the false Iranian claims of US casualties.

This may be it, or -- more likely -- it may herald a slower-brewed retaliation against other, softer targets, by proxies or covert forces -- the retaliation most analysts were expecting.

But this is not a reason to be cheerful. Yes, both sides may have steered deliberately away from a long and messy conflict. Yet they have also both learned they can attack each other directly.

They have both done things that were perhaps unthinkable a week ago. That is not good news. The tone of this morning may be de-escalatory. But the US and Iran had to get to a much darker place than they've seen in decades to choose calm.