A load has shifted too far toward the rear of the trailer, leaving too little weight on the vehicle's steering axle. What problem does the CDL manual say this causes?

49 CFR 383.111(a)(16); AAMVA CDL Manual (nhcdm.pdf) Section 3.2.4, p. 3-2

Where weight sits over the axles changes how the truck actually drives, not just how much it weighs overall. A steering axle that's too light can make the front end feel unpredictable and harder to control, which is exactly the opposite of what a driver wants in an emergency.