Congress probably allowed the bombings in some overly large bill that gave expansive power to the administration to interpret threats to the US as it sees fit. The war equivalent of the Chevron ruling.
https://en.wikipedia.org/wiki/Authorization_for_Use_of_Milit...
Remember when a bunch of people were complaining that tons of that legislation was dangerous crap that handed way too much power to the executive? Yeah, they were 100% right.