The trailer is resting on the tractor and the front trailer supports are up. What should you make sure that?

Step 15: Raise the Front Trailer Supports (Landing Gear)
When the full weight of the trailer is resting on the tractor:
- Check for enough clearance between the rear of the tractor frame and the landing gear. (When the tractor turns sharply, it must not hit the landing gear.)
- Check that there is enough clearance between the top of the tractor tires and the nose of the trailer.
[California Commercial Driver Handbook]