All this time Banks bore with him Halleck's instructions of the 9th of November, and more than once studied with care and solicitude these significant words: "As the ranking general in the Southwest you are authorized to assume the control of any military force from the upper Mississippi which may come within your command. The line of division between your department and that of Major-General Grant is, therefore, left undecided for the present, and you will exercise superior authority as far north as you may ascend the river." By the articles of war, without these words, Banks would have been entitled to the command they gave him, but the words showed him plainly what was expected of him by his government. To the incentives of patriotism and duty were thus superadded one of the most powerful motives that can affect the mind of the commander of an army,--the hope and assurance of power and promotion. If, then, he held back from joining Grant in Mississippi, it was because he hesitated to take the extraordinary risks involved in the movement. In this he was more than justified.
Since the miscarriage of Sherman's attempt at the beginning of the year, Grant had been engaged in a series of tentative efforts, steadily prosecuted in various directions, yet all having a common object, the finding of a foothold of dry ground for a decisive movement against Vicksburg. Four of these experimental operations had failed completely, and Grant was now entering upon a fifth, destined indeed to lead to a great and glorious result, yet in itself conveying hardly more assurance of success than the most promising of its predecessors, while involving perils greater than any that had been so far encountered. Of these, the greatest danger was that the enemy, after allowing him to land on the east bank of the river and to penetrate, with a portion of his army, into the heart of Mississippi, might then concentrate all the available forces of the Confederacy in that region and fall upon him with vigor at the moment when his supplies should be exhausted and his communications interrupted. In such an event the fortune of war might have rendered it imperative for him to retire down the river; but what would have happened then if Banks, disregarding Port Hudson in his eagerness to join Grant before Vicksburg, should in his turn have abandoned his communications? Both armies would have been caught in a trap of their own making, whence not merit but some rare stroke of luck could alone have rescued either.