Iran's Islamic Revolutionary Guard Corps displays in Tehran on June 21, 2019, what it says is wreckage from a U.S. drone its forces shot down. (Tasnim News Agency/Reuters)

In tweets Friday morning, Donald Trump explained how he had been about to retaliate against Iran’s shooting down of an American drone but decided to cancel the action at the last moment when he was told that there were likely to be 150 deaths. I asked a number of international relations scholars with relevant expertise to explain the logic of how we got here.

Erik Lin-Greenberg is an assistant professor at American University’s School of International Service who works on drone warfare. He notes that Iran’s choice of target may have been intended to communicate the country’s seriousness.

“Although Iran’s decision to target a remotely piloted aircraft (RPA) instead of an inhabited aircraft is significant, so, too, was its decision to target an MQ-4C Triton using a surface-to-air missile. First, the Triton is far more expensive and fewer in number than other RPAs, like the MQ-9 Reaper that routinely operate in the region. Choosing to target a pricier asset could mean that Tehran hoped to send a stronger signal of its displeasure with U.S. policies and actions. Second, downing the Triton with missiles instead of a less overt approach — like the electronic hack that Iran reportedly used to capture an RQ-170 drone in 2011 — also suggests that Iran intended to send a clear strategic signal to Washington.”

Susan Hannah Allen and Carla Martinez Machain are associate professors of political science at, respectively, the University of Mississippi and Kansas State University. They talk about Trump’s choices.

Trump’s tweet illustrates how leaders use a “menu” of foreign policy choices. In this case, Trump had (at least) two different options: escalating with airstrikes; or sticking with (increased) sanctions, to retaliate against Iran’s aggression. The choice to not use airstrikes is expected, since they tend to be used in low-salience crises, but choosing sanctions is unexpected, since those are unlikely in a high-stakes (potential war with Iran) confrontation. This may be explained by his discussion of the risks of a disproportionate response, in which collateral damage and casualties can increase the expected cost of airstrikes and make them less appealing to leaders.

Kenneth Schultz is a professor of political science at Stanford University. He explains the importance of proportionality.

The decision to use military force is a difficult one, and presidents can and should have room to change their minds. What is striking about last night’s events is how President Trump publicly sought to explain his decision not to pull the trigger on an operation that was “cocked and loaded.” Recent research in political science has sought to understand how leaders can manage the domestic political effects of backing away from a threat to use force, such as by invoking new information or imposing economic sanctions as a substitute. While Trump resorted to both strategies in his Friday morning tweets, what was unusual was his appeal to “proportionality”: the concern that killing 150 Iranians was a disproportionate response to the downing of an unmanned aircraft. Recent work suggests that Americans’ commitment to proportionality is not particularly strong, particularly if the targets are associated with the adversary’s military. But Trump benefits from the fact that Republicans are willing to give him political cover, while Democrats are more likely to criticize the process than the ultimate decision not to use force. This situation gives Trump a good deal of flexibility, but it also amplifies uncertainty and volatility in U.S. policy

Jason Lyall is an associate professor of political science and director of the Political Violence Fieldlab at Yale University. He notes inconsistency in Trump’s analysis.

This morning’s tweetstorm by President Trump about Iran is a wonderful example of the myth of the “paper tiger”: the dangerous, usually mistaken, belief that an opponent is both hellbent on aggression and easily cowed by military action or the threats of its use. Over the span of four tweets, Trump demonstrates remarkable intellectual flexibility, with Iran viewed as everything from a massive threat to the world to a boxed-in has-been (“bust,” in Trump’s words). The first tweet lambastes President Barack Obama for appeasing a looming Iranian threat. By the second tweet, Iran is now a badly weakened opponent. But dangerous enough to warrant a multisite retaliatory strike (tweet 3), unless civilians are harmed, in which case Iran isn’t that pressing after all. The fourth tweet is the real masterwork, though. Trump simultaneously argues that Iran is fading, that the United States holds all the cards and that there’s “no hurry,” except that Iran’s nuclear ambitions threaten the entire world, justifying a public pledge that Iran will “never” acquire these weapons. Given these inconsistencies in threat assessment, it is no wonder that the policy process appears dysfunctional and subject to capture by personalities and political considerations within the Oval Office.

Austin Carson is an assistant professor of political science at the University of Chicago. He asks what Trump’s motivations were for calling off the retaliatory action.

For me, the $64,000 question is: What underlies Trump’s concern about whether a strike with human fatalities would be a proportionate response to Iran’s attack on a pilotless drone? Perhaps because a disproportionate retaliation would be illegal under the laws of war? Or he worried about human suffering, or U.S. reputation, or the possibility that it would kick off an escalatory spiral where Iran would respond in turn? Or simple reelection concerns?

We have no way to know at this point, but my money is on escalation. Trump was surely briefed on how different U.S. responses would affect the likelihood of a violent Iranian response. Given Iran’s own rhetoric and its leadership dynamics, a U.S. attack that led to triple-digit casualties would almost certainly lead Iran to try to retaliate in kind. Even a limited tit-for-tat exchange would create an intense, months-long crisis that would seize attention Trump clearly would prefer to have focus on other things (i.e., immigration and the economy). He likes to raise the temperature through “maximum pressure,” but this would be a whole new ballgame.

Of course, this assumes Trump’s decision was reasoned and not pure impulse. Here I think it’s important to remember that gut reactions, intuition and strategy are not at all incompatible. Trump’s decision may have been a somewhat impulsive gut reaction which reflected his intuition that “this could get messy.” Trump need not be trained in game theory to understand an escalatory spiral would be likely and might damage him politically, which is what he most likely cares about the most.

Rose Kelanic is an assistant professor of political science at Notre Dame. She said that Trump may have lucked into the right response.

Trump stumbled onto the right policy — avoiding war — but the bizarre last-minute change in plans will surely confuse Iranian leaders. Avoiding unwanted escalation is hard enough when both sides strategically signal restraint. Trump signals randomness. Policy by Magic 8 Ball? Speculators might bid up oil prices in the short run, but even if war occurs, long-run supply disruption remains unlikely. And remember, 4 billion barrels of U.S. and allied strategic petroleum reserves (SPRs) can compensate for gaps.