Well, the bombings of the "drug smugglers" in the Gulf and Pacific are of very questionable legality. I'd say illegal unless I see a better justification than what Trump has given.
The DOD lawyers have apparently written a memo (not released to the public) providing this justification (which is quite different from Trump's public one):
- Drug smuggling activity funds the Mexican/international cartels, which in turn have been characterized as international terrorist organizations; hence, the bombings are aimed at international terrorism. It's a very, very shaky theory that's never been tested in anyone's courts.
Trump's justification is just flat-out not a justification at all.