...e Mississippi Central railroad, until, by getting near enough to threaten Vicksburg, he should compel the evacuation of that place. A cooperative movement, by troops from Helena, in Arkansas, which Halleck ordered, was intended to cut the railroad in Pemberton's rear and threaten Grenada. On the 23d, Halleck again broached the subject of the river expedition, doubtless urged on by the President, wh...