Behold, I will put a spirit in him, so that he shall hear a rumor and return to his own land, and I will make him fall by the sword in his own land.’”
The contents of Rabshakeh's speech being brought to Hezekiah, one would have expected (and it is likely Rabshakeh did expect) that he would call a council of war and it would be debated whether it was best to capitulate or no. Before the siege, he had taken counsel with his princes and his mighty men, Ch2 32:3.
Commenting on 2 Kings 19:1-7
Behold, I will send a blast upon him, and he shall hear a rumour, and shall return to his own land; and I will cause him to fall by the sword in his own land. (d) The Lord can with one blast blow away all the strength of man, and turn it into dust.
Behold, I will send a blast - and he shall hear a rumor - The rumor was, that Tirhakah had invaded Assyria. The blast was that which slew one hundred and eighty-five thousand of them in one night, see Kg2 19:35. Cause him to fall by the sword - Alluding to his death by the hands of his two sons, at Nineveh. See Kg2 19:35-37.