During this period, the overland half of Grant's offensive was also failing. His lines of communication were disrupted by raids by Brig. Gen. Nathan Bedford Forrest and by Maj. Gen. Earl Van Dorn, who destroyed a large supply depot in the Holly Springs Raid on December 20. Unable to sustain his army without these supplies, Grant abandoned his overland advance. Sherman realized that his corps would not be reinforced by Grant and decided to withdraw his expedition, moving to the mouth of the Yazoo on January 2. On January 5, Sherman sent a letter to General-in-Chief Henry W. Halleck, summing up the campaign (in a manner reminiscent of a famous statement by Julius Caesar), "I reached Vicksburg at the time appointed, landed, assaulted, and failed." He and his command were then temporarily assigned to Maj. Gen. John A. McClernand for an expedition up the Arkansas River and the Battle of Arkansas Post. Although Grant tried a number of operations, or "experiments", to reach Vicksburg over the winter, the Vicksburg Campaign did not begin again in earnest until April 1863.