Since the storming of the American Embassy in Tehran (and the seizing of the aforementioned 52 hostages) in 1979, the two countries have been in a low-grade or proxy conflict. Since then, General Suleimani spent 22 years at the helm of Iran’s own Quds Force as Tehran’s liaison to countless militias, factions and terrorist groups across the Middle East, except for brief moments of calm, such as when General Suleimani offered to help American troops attack his enemy, the Taliban, in the wake of the 9/11 attacks, only to rebuff cooperation after President George W. Bush lumped his nation in with Iraq and North Korea as part of an axis of evil.

Yet there was a reason that past American presidents refrained from assassinating one of the region’s most powerful and, yes, blood-soaked military commanders: Iran’s ability to respond with asymmetric violence.

The regime has turned that stratagem into an art form since the catastrophic war with Iraq during the 1980s, which at times resembled the slaughter at the Somme. General Suleimani saw combat then and learned some of the lessons that guided his doctrine of proxy fighting from Yemen to Lebanon.

By declaring that the United States will respond with airstrikes to any attacks on American targets or assets, Mr. Trump is drawing a bright red line that Iran cannot cross. And yet, Iran relies on a network of proxy actors from Yemen, Syria, Iraq and Lebanon. Must they all respect Mr. Trump’s red line? There are plenty of hotheads in those proxy forces that will be incensed by the assassination, the same way young men with weapons and minimal discipline often are. Even during the Iraq war, which saw the deaths of hundreds of American soldiers from Iranian munitions, keeping proxy militias under control was difficult.

Mr. Trump can’t keep an entire region from crossing his red line, making violent conflict all the more likely if the president holds to it. And Iran itself can respond less directly, but no less effectively, with cyberwarfare, attacking American allies in the region, disrupting trade and undermining the United States in Iraq and elsewhere.

A senior national security official told The Atlantic in 2018 that the administration believes that “permanent destabilization creates American advantage.” Mr. Trump may well be creating permanent destabilization, but that is to no one’s advantage and such loose talk may just be rationalizing a lack of planning and reason.

Mr. Trump’s national security staff has thinned out drastically in the past year or so. Seasoned counsel may be either in short supply or given little credence.