Apparently Qasem Soleimani was a key leader in the Iranian military:
As leader of the Islamic Revolutionary Guard Corps’ elite Quds Force, the 62-year-old bore responsibility for Iran’s clandestine operations abroad, quietly extending the military reach of Iran deep into foreign conflicts such as those in Syria and Iraq.
In the process, he earned himself near-mythical status among his enemies and idolization by his Iranian hard-line supporters.
Analysts have complained that Soleimani had more diplomatic clout than Iranian Foreign Minister Mohammad Javad Zarif and pondered whether he would eventually seek top political office. Some compared him to Karla, the fanatical, but fictional, Soviet spymaster in John le Carré’s Cold War novels.
Killing him was a major provocation, and certainly it will have some effect on the morale and capabilities of the Quds Force, but is it going to have any long-term effect? My guess is that it won’t, for two reasons. First, military and paramilitary organizations are designed to be resilient to loss of command since one of the major risks of war is, obviously, death. Second, the command structure of any quality military organization is going to be full of ambitious and talented officers who are capable of taking the place of the top leader.
In other words, there are half a dozen Karlas waiting in the wings to replace this guy. The history of this endless war is replete with the killing of some #1 or other that probably causes some short-term chaos, but changes very little in the long run. I think part of the reason that the US is constantly “decapitating” enemies is that we can do it with precision airstrikes rather than a commitment of ground troops, so it is a relatively easy gesture that shows we’re “doing something”.
Well, now we did something. As much as Trump, Pompeo and the rest want to do more, that next steps are a hell of a lot more militarily and politically risky than a targeted airstrike.