Originally Posted by Unca_Sam

I'm very confused by what looks like pitting on what should be an aluminum stem (right there under the bar clamp bolt). There also should not be any rust at the handlebar/stem clamp interface. Are the bars steel? A magnet is your friend here.

I would try a torch to the bolt (enough to make it too hot to touch) before I used a wrench with a hammer. If that clamp was assembled without grease, you could also be facing the dreaded aluminum weld that locks stems and seatposts inside bike frames.