Psalms 36:12 - Joseph Benson’s Commentary on the Old and New Testaments

There are the workers of iniquity fallen There, where they came against me, and hoped to ruin me. He seems, as it were, to point at the place with his finger, as if their downfall were already effected, and he could tell all the circumstances of it. Upon the very spot where they practise their treachery, they receive their downfall, which is the proper force of the word שׁם, sham, as אז, az, denotes the very instant of time.