The DEA for a long time has been slowly transforming into this catch all military/police/spy/logistics/legal/intelligence/technical agency. It picks up little bits of responsibility and capability here and there that enable it to do some function in a drug case. But because the funding of drug law enforcement is so crucial for so many government functions in direct and indirect ways, and because individuals in a position often benefit from an increase in scope the pressure is always towards scope creep, to saying yes when permission for more power is asked.
So the DEA has organically expanded and expanded and expanded and the more this is accepted the easier it is for it to creep further and further until it starts to resemble something totally different than how it would have originally been envisioned.
On the other side of this you get someone like Trump, who is looking for tools he can use that have limited restrictions on their powers and a wide scope of arenas in which they can be deployed, and the DEA is an obvious choice.
An you end up with a very dangerous combo of a person who is looking for as much power as he can grab onto and this entity which is incredibly efficient and capturing scope and power within our current system and therefore extremely ripe for abuse.
This is a great argument for strictly defining the scope of these alphabet soup agencies upfront and making the process to change those scopes very restrictive. Unfortunately we've chosen the exact opposite path.