This should be an easy one.
Picked up a Cinelli stem from the Co-op for some Cinelli bars I have (26.4).
Someone tightened the handlebar bolt down, and I can't unscrew it enough to remove it or get handlebars in. Turning the bolt from the back only causes the front to spin:
I tried leveraging the stem "open" as I unscrew to give some more purchase to the nut, but hard to do with just two hands and also makes it difficult to apply the right amount of pressure that lets me turn the bolt.