Originally Posted by zebede

If it is like some of the Dahons, The stem is clamped to the steer tube. But before you can loosen the clamp and rotate you must first fold the stem and loosen the large nut that is threaded internally to the steer tube. This large nut also adjusts headset bearings. Very similar concept to threadless headsets but the star fangled nut is replaced by internally threaded steer tube w/nut.

FWIW that brass bolt looks dangerous, At a minimum I would cut it off and dress it with a file, or find a donor quick release seat type clamp, which is what was there in the first place.