Although I dont know the limitations of the application of fetanyl, I do know that ba absorbed through the skin.
That means any surface you touch could end up killing you.
I think the Russians used an aerosolized version and pumped it into the ventilation system. It could also easily be pulverized into fine powder and dispersed via many various means - I’m not sure if it is soluble in water and if it is whether water supplies could be contaminated. It could be done simultaneously across many geographic locations by organized terrorist cells like the 9/11 hijackers did with multiple planes (and presumably there were more planes, but the FAA grounded all flights quickly). It could be used not just on humans but on farms to kill livestock, too.
This is why the border needs to be secure. I feel bad for people who feel forced to flee their homelands but all this fentanyl coming across is a menace; it is already being weaponized by drug cartels by lacing it into seemingly more innocuous drugs and counterfeit pills.
Read this :
It is a common misconception that fentanyl can be absorbed through the skin, but it is not true for casual exposure. You can't overdose on fentanyl by touching a doorknob or dollar bill. The one case in which fentanyl can be absorbed through the skin is with a special doctor-prescribed fentanyl skin patch, and even then, it takes hours of exposure.
https://health.ucdavis.edu/news/headlines/can-fentanyl-be-absorbed-through-your-skin/2022/10