Since they were designated as a foreign terrorist organization, then he's legally allowed to execute them without a trial.
Ignoring the second part (which is not as simple as you make it sound, e.g. there needs to be imminent danger, lack of other options such as arrest etc), who's "they" and who "designated" them? It doesn't look like there were any names published, let alone proof of them being terrorists.
Sounds like a load of BS orchestrated to make it seem like the US is "at war" with some gang so that the DOJ can use this in their deportation cases by "designating" people as being members of said gang.
11 drug kingpins
Oh they're kingpins now. 11 of them. On a boat somewhere in the Caribbean. I'm sure you have proof of that but just too busy to post it.