The toughest drug enforcement agency in the United States is the IRS, that is the Tax Bureau, and the second toughest, which is the professional counterpart, is the DEA.
How does the DEA do its job? Well, let's just say if the DEA was really doing a great job, then those junkies wouldn't be occupying the streets of America.
But the DEA really does have a lot of power, especially since they have the authority to enforce overseas, in Mexico, in Ecuador, the DEA has offices. If they want to hit someone, just tossing a bag of flour onto their car is enough.
The U.S. military is formidable, but unless it's a formal invasion of another country, don't even think about conducting any military actions openly on foreign soil.
So, when the DEA and the Special Forces come together, it's the best of both worlds.
The Phantom Brigade relies on the DEA to provide excuses for real combat opportunities, and since the DEA can't fight by itself, it depends on those Special Forces as enforcers.