Here is a little more on the subject. FC
"Halleck established an uncomfortable relationship with the man who would become his most successful subordinate and future commander, Brig. Gen. Ulysses S. Grant. The pugnacious Grant had just completed the minor, but bloody, Battle of Belmont and had ambitious plans for amphibious operations on the Tennessee and Cumberland Rivers. Halleck, by nature a cautious general, but also judging that Grant's reputation for alcoholism in the prewar Army made him unreliable, rejected Grant's plans. However, under pressure from President Lincoln to take offensive action, Halleck reconsidered and Grant conducted operations with naval and land forces against Forts Henry and Donelson in February 1862, capturing both, along with 14,000 Confederates.[10]

Grant became a national hero, delivering the first significant Union victory of the war. Halleck obtained a promotion for him to major general of volunteers, along with some other generals in his department, and used the victory as an opportunity to request overall command in the Western Theater, which he currently shared with Maj. Gen. Don Carlos Buell, but which was not granted. He relieved Grant of command after Grant met with Buell in Nashville, citing rumors of renewed alcoholism, but pressure by Lincoln and the War Department caused him to revert his decision; as he explained the reinstatement to Grant, Halleck portrayed it as his effort to correct an injustice, not revealing to Grant that the injustice had originated with him. Nevertheless, Halleck designated one of Grant's subordinates to lead a follow-up operation down the Tennessee and personal intervention from Lincoln was again required to restore Grant to full command.[11] When Grant wrote to Halleck suggesting "I must have enemies between you and myself," Halleck replied, "You are mistaken. There is no enemy between you and me."[
(from Wikapedia)