Is the jackscrew holding leading edge UP?, or DOWN? in 400 knot cruise??
Basic aero: the horizontal stab is an upside down wing, and produces downward force. A lifting body wants to pitch down from its direction of lift. That's why the stab "wing" pushes down on the back, to keep the main wing from pitching down. Since the stab itself is pushing down, it wants to rotate in a direction that would pitch its leading edge up. So the control system must maintain a leading edge down torque on the stab.
In consequence, if the jackscrew failed, the result would be a prompt and very violent nose-down aircraft pitch.
This happened to a Navy A-6 Intruder in 1990 during flight tests; the stab linkage failed at about 400 kt and resulted in an instantaneous -6g pitchover. Capt Hazelrigg was killed in the crash; at 1,500 ft AGL there wasn't time to eject.