Harold Hongju Koh, a well regarded professor of international law at Yale Law School says (in the FT):
'Trump has baldly violated the UN charter, with no valid claim of self-defence & engaged in an illegal extraterritorial arrest that will be vigorously contested in a US court... All on the pretext of stopping drugs, when his transparent goal is profiting from oil'!
As Koh argues this will ultimately be a test of the legality of the US' assertion of extraterritorial sovereignty!