President Lincoln demoted McClellan because C. McClellan failed to defeat Lee at Antietam Creek. McClellan also failed to pursue Lee after the Battle of Antietam despite Lincoln's commands.
C. McClellan failed to defeat Lee at Antietam Creek.
Explanation:
Abraham Lincoln removed McClellan in 1862 from the command of the Army of Potomac because he was not able to beat General Robert Lee’s Confederate Army. Although McClellan was able to build a strong army, he dismissed a series of Lincoln’s suggestions and when Lee attacked the army he retreated even when his army outnumbered the Confederacy army.
