The definition used by the State Department for designating foreign terrorist organizations in the Antiterrorism and Effective Death Penalty Act of 1996 says “the term ‘terrorism’ means premeditated, politically motivated violence perpetrated against noncombatant targets by subnational groups or clandestine agents; the term ‘terrorist group’ means any group practicing, or which has significant subgroups which practice, international terrorism” (Section 2656f(d), Title 22, U.S. Code). It is far from clear that cartels’ motivation is political rather than financial.
It appears that Mr. Trump was making another political statement without checking the law. When the law was drafted by the Justice Department and State Department Counterterrorism Office, where I worked on the issue at the time, there was no discussion of including drug cartels. The target was various politically motivated groups such as the Abu Nidal organization and Hamas.