C. F. Keil and Franz Delitzsch on 2 Samuel 17:12

2Sa 17:12 “And come we to him (if we come upon him) in one of the places where he is found, we let ourselves down upon him, as the dew falls upon the earth; and of him and all the men with him there will not be one left.” נחנוּ might be a contraction of אנחנוּ, as in Gen 42:11; Exo 16:7-8, etc.: “so we upon him,” equivalent to “so shall we come upon him.” But if this were the meaning, we should expect עליו והינוּ. It is more correct, therefore, to take נחנוּ ekat ot  as the first pers. perf. of נוּח, as the early translators have done: so do we let ourselves down upon him. (For נוּח as applied to an army encamping, see Isa 7:2, Isa 7:19; and as denoting the swarming of flies and grasshoppers, Isa 7:19 and Exo 10:14.) In Ahithophel’s opinion, it would be possible with a very small army to crush David and his little band, however brave his followers might be, and in fact to annihilate them altogether.