So far, the legal interpretation of the AUMF has been stretched far, but not that far. It is what allowed for military operations against ISIS. Congress never approved it, but by continuing to pass a defense budget that funds AUMF operations, it is interpreted as tacit approval (therefore, no lawmakers have to attach their names to either side of the issue). It’s a controversial interpretation, but so far it has not been challenged.

The AUMF grants authority to conduct military operations against, paraphrasing here, “those responsible for the attacks on September 11th.” This was defined as Al Qaeda and its affiliates (most notably Al Qaeda in Iraq, which later became ISIS). Did ISIS have anything to do with 9/11? No. Are they an AQ affiliate? Not really. AQI was an affiliate, in that they were funded by and took orders from AQ. There’s a lot of documented history that I’ll skip over, but basically AQI became ISIS, and there was a major dispute between the leadership of AQ and ISIS that resulted in the two groups being at war with one another. Nevertheless, the historical link is what is being used to classify them as an affiliate, and the affiliate status is what is being used to characterize them as “those responsible for 9/11.”

Could that same justification be used against Iran, or more specifically the IRGC? The only possible link I can think of is that there is evidence that Hezbollah may have provided material support to Al Qaeda - specifically, in the 1998 East African embassy bombings - and there is significant evidence that Iran has supported Hezbollah’s terrorist activities. There may be more classified intel that the public isn‘t aware of, but in my opinion the use of AUMF here would not hold up to legal scrutiny - but then again, it hasn’t ever faced any.

Source: educational background in national strategy policy