1:11 From you came one
who plotted evil against the LORD,
a worthless counselor.
v.9 asks, "What do you [plural] plot against the LORD?" Here, Nahum uses "you" [feminine singular] in the Hebrew which means he's speaking directly to the Assyrian capital city, Nineveh*. The "one who plotted evil" and the "worthless counselor" is a product of Nineveh.
Sennacherib made Nineveh the capital city of the Assyrians, so this verse could be speaking about a king that came after him.
Any leader who is against God is nothing short of worthless. Any person in general who is against God is worthless in their counsel and example.
*see Daily Devo #9. Cities in Hebrew are referred to in the feminine. The "tsarah" in v.9 could be a female adversary, Nineveh itself.