Lincoln paid a visit to McClellan on October 1, 1862, during which he urged the general to act energetically, crossing the Potomac, but the Army of the Potomac was put in motion to cross the river only on the 26th, after a peremptory request of both Halleck and Lincoln.
That he failed to pursue Lee after Antietam.
Lincoln was disappointed that General George B. McClellan had allowed Confederate general Lee to escape after the Battle of Antietam. The result of Lincoln's disappointment was the replacement of McClellan by General Burnside.
Based on his previous actions, and not just those at Antietam, Lincoln fired Major General George McClellan as general-in-chief of the Union armies and replaced him as commander of the Army of the Potomac with Ambrose Burnside.Lincoln was likely prompted by what he saw as the indecisive, overcautious nature of McClellan, who at Antietam thought that he was outnumbered when it was very much the reverse.
Major General George B. McClellan was unaware that President Lincoln wanted to replace him. McClellan and his War Democrat supporters considered McClellan the hero of Antietam. By the end of October 1862, McClellan had rebuilt his Army of the Potomac to 120,000 troops. He had only 70,000 troops at the battle of Antietam.
At the camp, President Lincoln was in a conversation with another politician. After referring to the Army of the Potomac, he made a joke. He said " excuse me, I was not referring to the Army of the Potomac, I meant to say " McClellan's bodyguard".
Because Lincoln felt that McClellan lacked the aggressiveness required to successfully defeat the Confederate army. McClellan was very meticulous and patient. He did not chase Confederate General Robert E. Lee after defeating his troops at Antietam. Lincoln got tired of McClellan's patience and decided to replace him with Ambrose Burnside.
After Antietam (Sept 17, 1862) when McClellan once again believed he needed time for his troops to rest. President Lincoln replaced him (on Nov 7) with General Ambrose Burnside. That was the end of McClellan's service as a Union military leader. As an aside, General Burnside felt uncomfortable replacing George B. McClellan. He had been loyal to him, also, he was not sure the command of the Army of the Potomac would be a fit for his abilities.
President Lincoln's preliminary Emancipation Proclamation in 1862 was a shock to General McClellan. He also was shocked when Lincoln soon after suspended habeas corpus. He was opposed to both of these actions by President Lincoln.
After the US Civil War Battle of Antietam, General George B. McClellan was unwavering in his stance to not reengage Lee's army in Virginia. Based on his correspondence with General Halleck, Secretary of War, Edwin Stanton and President Lincoln, McClellan gave his reasons for not advancing. His rational was that his troops were unprepared in numbers, organization, morale, supplies and equipment to renew the battle against General Lee. Therefore, McClellan refused to follow Lincoln's direct order to advance. In his own words he stated in part that " these people don't know what an army requires and therefore act stupidly..."What is missing from the events following the Battle of Antietam seems to be contrary information from any of McClellan's generals. What is also missing is any information from the Confederate side on any aspect of the McClellan-Lincoln controversy.
When the US Civil War Battle of Antietam ended on September 17, 1862. Two major events took place. First was Lincoln's issuance of his preliminary Emancipation Proclamation. Also, in November, General George B. McClellan was relieved of his duties by president Lincoln.
When General George B. McClellan returned to Washington DC on March 11, 1862, he became aware that President Lincoln removed his title of general in chief.
Because he had caused so many delays tha some of Lincoln's cabinet were starting to doubt his loyalty to the cause, and after the Battle of Antietam, he failed to pursue and destroy the enemy.