A driver feels the trailer begin to skid after braking hard. According to the AAMVA manual, what is the correct way to stop the skid?

AAMVA CDL Manual, Section 6.1.5 "Prevent Trailer Skids," p. 6-2-6-3, Figure 6.2

The instinct under panic is to brake harder, but with a trailer skid that instinct makes things worse because locked trailer wheels are what started the skid. Releasing the brake to let the tires regain grip is counterintuitive, which is exactly why it has to be learned before it is needed on the road.