During the Civil War, Lincoln employed four commanding generals of the Union Army: Winfield Scott, George McClellan, Henry Halleck and Ulysses S. Grant. President Lincoln famously despaired of the Union leadership during the early part of the war, until Grant's appointment to the post and subsequent victories.
Winfield Scott commanded the Union armies at the outbreak of war and urged caution rather than a rushed attack into Virginia. When Lincoln countermanded his plan and the attack failed, Scott resigned. Lincoln then appointed George McClellan, whose greatest fault was overestimating the Confederates and refusing to act until he felt he was properly supplied and reinforced. Lincoln replaced him with Henry Halleck, only to discover Halleck did a poor job of managing his generals. It was only after the appointment of Ulysses S. Grant, following his victories in the West, that the Union found a capable general-in-chief.