Adam Clarke on Isaiah 37:8

Rabshakeh returned - From Isa 36:2, we learn that the king of Assyria had sent Rabshakeh from Lachish to Jerusalem; now it is likely that Rabshakeh had besieged that place, and that the king of Assyria had taken his station before this city, and dispatched Rabshakeh against Jerusalem. But, as in the verse above it is said, "he had departed from Lachish," probably he had been obliged to raise the siege, and sat down before Libnah, which promised an easier conquest.