If memory serves, President Lincoln was pretty sure that a win by the opposition in the '64 election would indicate a shift in public will from victory in war, to peace at any price. He was prepared, in the event that he lost his bid for a second term, to assist the new President-Elect in seeking this end.
In all honest, I do not see a President McClellan being able or willing to prosecute that war as President Lincoln was. I simply do not see the Union winning.
By now, I have given up on persuading people that McClellan would not have accepted disunion--no matter how many times I quote his explicit statements to that effect ("... the Union must be preserved at all hazards. I could not look in the face of my gallant comrades of the army and navy, who have survived so many bloody battles, and tell them that their labors and the sacrifice of so many of our slain and wounded brethren had been in vain; that we had abandoned that Union for which we had so often periled our lives...no peace can be permanent without union."--just how explicit does he have to get?!) they say that he didn't really mean it, or that he couldn't have continued the war even if he wanted to, that it would be politically impossible to do so. To which William Freehling IMO has convincingly replied that McClellan could not afford *not* to win the war--after all, those who favored the restoration of the Union, by war if necessary, would be a decisive majority of the Northern people (virtually all Republicans plus a large percentage--almost certainly a majority--of Democrats). Even the Chicago platform talked about restoring the Union on the basis of "the federal union of the states"--and even if one (dubiously) regards it as a peace-at-any-price platform, McClellan repudiated it as so interpreted.
But let's assume that Lincoln was right when he said McClellan could not preserve the Union--unless it had already been 'saved" before he took office. I will here reproduce an old soc.history.what-if post of mine:
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Lincoln's confidential cabinet memo of August 23, 1864, which spoke about
saving the Union between the election and the inauguration was written
*before* McClellan made it clear that he would not accept any peace without
reunion. Even apart from McClellan's stated reason for this position--that
he could not look his old comrades in the face otherwise--sheer political
necessity would have required McClellan to pursue the war to the end, as I
have discussed in a previous post. Nevertheless, let's say that (a)
Lincoln is still convinced in November that McClellan could not save the
Union, and (b) that McClellan wins. The question is how Lincoln would
"save the Union" before Inauguration Day. Wiliam C. Davis makes an
interesting speculative analysis of this in his chapter "The Turning Point
That Wasn't: The Confederates and the Election of 1864" in *The Cause
Lost: Myths and Realities of the Confederacy* (University Press of Kansas
1996). What follows is based on Davis' analysis.
If Lincoln had been defeated, we must assume that it was because Sherman
failed to take Atlanta by early November. There are only three logical
reasons why that might happen: (1) Sherman was vigrously attacked and
pushed back in late spring or early summer by Joseph E. Johnston before
penetrating deep into Georgia. This is so completely out of character for
Johnston that it may be dismissed as too implausible. (2) The Yankees
invested Johnston or his successor Hood in Atlanta and had the Confederate
commander virtually surrounded and under siege but had not taken the city.
(3) Sherman was driven back from Atlanta's outskirts by desperate and
costly assaults in the summer by Hood.
Now either (2) or (3) (dismissing (1) as implausible) still leaves Sherman
with the upper hand in Georgia. Even if Hood had pushed Sherman away from
Atlanta, it would have been at the cost of crippling casualties to the Army
of Tennessee, as is demonstrated by the assaults Hood did launch during the
battles for Atlanta and in the subsequent Tennessee campaign. Thus
Sherman, with numerical and logistical superiority, could have divided his
command, left part of it to hold a weakened Hood in Georgia and sent the
rest to Virginia. If, however, Hood had been besieged, Sherman would have
had more than sufficient troops to man his own trenches while detaching up
to 40,000 men to help Grant take Richmond by March 4. As William C. Davis
remarks:
"Whether Sherman sent them by rail through Chattanooga and the North, or
overland, where there were no Confederate forces to impede their progress,
in any case Grant could have had a reinforcement of fresh troops in numbers
equal to Lee's entire army available before the end of the year. Grant
would have opted for the overland route, which, though slower, would still
have had Sherman approach Lee from the southwest, thus cutting off Lee's
only route of retreat from Petersburg. Contrary to popular misconception,
Atlanta was always an expendable objective for Grant...
"What we have then are Lincoln's determination to win before March 4,
Grant's determination that Richmond and Lee were psychologically the
decisive targets, and Sherman's ruthless dedication to punishing the
Confederacy, along with the availability of his large army, relatively
fresh, seasoned at hard marches, and not worn down and exhausted like the
Army of the Potomac. Whether surrounded and overwhelmed in the trenches,
or cut off on an attempt to break out and retreat, Lee, his army, and
Richmond as a result would inevitably have fallen before March 4. The only
imaginable alternative to this scenario is the inconceivable notion that
Lincoln, Grant, and Sherman would all suddently have run against type,
turned their backs on the convictions and plans they had expressed
repeatedly in 1864, and sat back and left the initiative to the
Confederates."
The fall of Richmond would not by itself necessarily have been the end of
the war--there would still be Hood's army in Georgia to mop up--but the end
would be so clearly in sight that it would be insane for McClellan to
snatch defeat from the jaws of victory. He had had few enough triumphs in
the war, and was hardly likely to deprive himself of the ultimate one.
