In a scenario where Sherman’s March doesn’t go well and Northern morale for the war is low, Lincoln loses reelection to George McClellan or any Peace Democrat that was willing to negotiate with the CSA. Lincoln has five months before the opposing candidate is inaugurated. So does Lincoln take this opportunity to continue the war and bring the CSA to surrender before the new president is inaugurated or would he save face and immediately negotiate terms with the CSA when he knows morale for the war is low.
Having thought on this more, I think it bares pointing out the March to the Sea didn't start until November 15 while the 1864 election was on November 8th; so the former could not affect the latter given the timeframe. If I may suggest such, I have been discussing a scenario with Saphroneth lately on this sort of setup i.e. last second Confederate victories resulting in a Lincoln defeat. My idea is Price's Missouri Expedition being successful, and this resulting in a Confederate victory at Cedar Creek. Price's campaign began on August 28th, although the first serious engagement did not come until late September. Cedar Creek, meanwhile, was not until late October and before that The Burning had happened, as well as the sentiment that Early was beat and the Valley secured. Therefore, Lincoln could order Sheridan to the West with VI Corps and the Calvary Corps, leaving the Army of West Virginia and XIX Corps for the Valley.
So, let's say by late September it's becoming obvious a disaster is brewing in Missouri and therefore Sheridan is shipped; let's say a month, so they're in action just before election day at the start of November. Early still attacks the rump Union force in the Valley but this time, there is no Cav to form a temporary defensive line and no VI Corps to rally around, so it's a complete rout. Early can, therefore, move into Maryland in late October as he had in July, sufficiently terrorizing the Administration that Grant is forced to make detachments. Say he sends IX Corps (15,845 men) and X Corps (14,609 men), given how he responded to Early's attempt in July, for a total of 30,454 men sent to Maryland; this reduces the Army of the Potomac (Inclusive of the Army of the James) to 60,633 men, based off it's October returns of 91,117 men present.
This parity in strength makes a Fort Steadman-style attack aimed at destroying City Point that much more likely to succeed as now there is not enough manpower left to Grant to organize an effective counter-attack without opening holes in his line elsewhere for Lee's command to exploit. Not only would the Army of the Potomac be extremely battered and incapable of offensive action, it's like they would have to conduct a serious withdraw, shortening the line and allowing Lee to reclaim the Weldon Railway, improving his logistics in addition to defensive prospects.