I had a post on this subject some years ago isn soc.history.what-if (my apologies for any links that no longer work):
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Atlanta doesn't fall--Lincoln wins anyway?
It is frequently assumed that if Atlanta had not fallen, Lincoln would have been defeated for re-election. It is often debated whether McClellan's winning the election would have made any difference to the outcome of the war; but that he *would* have won, had Atlanta not fallen, seems to be a widely held belief.
To pose the issue in terms of electoral votes: McClellan would have won if he had carried every state which Lincoln in OTL won by 54.4 percent of the vote or less.
http://psephos.adam-carr.net/countries/u/usa/pres/1864.txt In that event, McClellan would have gotten 123 electoral votes to Lincoln's 110. (The seven states that would shift in this scenario would be Connecticut, Illinois, Indiana, New Hampshire, New York, Oregon, and Pennsylvania, with a total of 102 electoral votes.)
So the question is: Would a failure to capture Atlanta, by itself, be enough to get 4.4 percent of the electorate to change its votes?
First of all, we must remember that this is *not* the same question as "If the election had been held in August rather than November, would Lincoln have lost?" (Lincoln himself certainly thought his defeat "exceedingly probable" in August.) After all, other things happened in that interval besides the fall of Atlanta:
"If the election had been held in August 1864 rather than November, Lincoln would have lost. . . . This did not happen, but only because of events on the battlefield--principally Sherman's capture of Atlanta, *and Sheridan's spectacular victories over Jubal Early in the Shenandoah Valley.* These turned northern opinion from deepest despair in the summer to confident determination by November." (James M. McPherson, "American Victory, American Defeat," in Gabor S. Boritt (ed.), The Collapse of the Confederacy (New York: Oxford University Press, 1992), 39-40. (Emphasis added.)
Even if we agree that Lincoln had to have a military victory to win in November, it is arguable that Sheridan's victories in the Shenandoah Valley would have been sufficient for this purpose. Albert Castel argues that they would not be enough to make up for the failure to capture Richmond or Atlanta, though he acknowledges that "no doubt Sheridan's victories would have boosted Northern morale and the Republicans would have made maximum political advantage of them." After all, he notes, the Democratic *New York World* pointed out that in spite of Sheridan's success "we hold no more of the valley than we did six months ago, nor than we have done several times in previous years of the war."
http://books.google.com/books?id=6d6hvQwOTiwC&pg=PA25 Well, a Democratic newspaper *would* emphasize the negative, wouldn't it? But the issue is how Sheridan's victory was *perceived* by people who were not die-hard Democrats, and there is considerable evidence that Sheridan's campaign thrilled Northerners; Thomas Buchanan Read's poem "Sheridan's Ride"
http://bartleby.com/102/150.html became enormously popular. In any event, given the close division of the electorate in a no-Atlanta-victory scenario, *any* substantial boost to Northern morale might have been enough to assure Lincoln's victory.
Second, we have to remember that getting four to five percent of the voters to change their minds was *very* difficult in the nineteenth century, when party loyalty was much greater than in our own time. "'[F]or military historians to be declared right that Sherman's victory alone could have saved Lincoln's victory, or that Lincoln's victory alone could have saved Union victory, political historians must be proved dead wrong about antebellum politics in general and the Democratic Party in particular.' [William W. Freehling, 'The Divided South, the Causes of Confederate Defeat, and the Reintegration of Narrative History,' *The Reintegration of American History: Slavery and the Civil War* (New York: Oxford University Press, 1994), 226-227] The former because 90 percent of 19th century American voters remained loyal to party, the latter because Peace Democrats were a minority within that party."
http://warhistorian.org/blog1/index.php?entry=entry050824-184753 (This post also notes that other historians besides Freehling who agree that Lincoln would have won even without the fall of Atlanta include William C. Davis and Larry J. Daniel. Daniel's 1998 essay in "North and South" magazine is apparently a point-by-point rebuttal to Albert Castel's "The Atlanta Campaign and the Presidential Election of 1864: How the South Almost Won by Not Losing." Castel's argument can be found at
http://books.google.com/books?id=6d6hvQwOTiwC&pg=PA15 Unfortunately, I can't find Daniel's rebuttal online.)
Third, there was the fiasco of the Democrats adopting a peace platform that their own candidate repudiated. IMO this platform would have been unpopular whether Atlanta fell or not. Most Democrats were not opposed to the war or willing to acquiesce in disunion. (One can argue that the platform was not really a peace-at-any-price platform, since, though it called for a cease-fire, it also called for "an ultimate convention of the States, or other peaceable means, to the end that, at the earliest practicable moment, peace may be restored *on the basis of the Federal Union of the States.*"
http://www.sewanee.edu/Faculty/Willis/Civil_War/documents/democratic.html [emphasis added] What matters, however, is that it was widely perceived, rightly or wrongly, as involving acquiescence in disunion as a practical matter.) What they were opposed to was what they considered the administration's incompetence in fighting the war. As Lincoln told Hugh McCulloch after the election, "I am here by the blunders of the Democrats. If instead of resolving that the war was a failure, they had resolved that I was a failure and denounced me for not more vigorously prosecuting it, I should not have been reelected, and I reckon you would not have been Secretary of the Treasury."
http://www.mrlincolnswhitehouse.org/content_inside.asp?ID=92&subjectID=2 So to the "normal" Republican vote--which one must remember was about half of the vote in the North even during bad years for the Republicans--you have to add those War Democrats who just cannot stomach the peace platform. They are a small minority of the Democrats, to be sure--most War Democrats will vote for McClellan (as will, despite their misgivings, almost all Peace Democrats). But the few who won't could be enough to turn the balance of the election even if Atlanta doesn't fall.
Fourth, although Castel mentions Atlanta as causing Fremont to withdraw his third party candidacy, Fremont would almost certainly have withdrawn anyway; as a committed emancipationist, Fremont would not have wanted to be the man who made McClellan's victory inevitable.
Fifth, Castel, citing Lincoln's own pessimistic view of his prospects in August, argues that it is arrogant for modern historians to think they know the political situation in 1864 better than so shrewd a politician as Lincoln knew it at the time. (As David Donald noted in *Lincoln Reconsidered*
http://books.google.com/books?id=_47AoFUWtQsC&pg=PA179 even as late as October, Lincoln calculated that he would win by only six electoral votes--three of them from Nevada, which had been admitted just for such an electoral emergency) But leaving aside the fact that, as I noted, Lincoln's August forecast was before the Democratic "peace platform," before Fremont's withdrawal, and before Sheridan's victories in the Valley, even the most politically shrewd presidents in the era before modern polls have underestimated the margins by which they would be re-elected. Theodore Roosevelt wasn't sure he would win on the eve of his 1904 landslide; Franklin D. Roosevelt thought that Jim Farley's forecast that Landon would carry only two states in 1936 was way too optimistic; etc.
My own guess is that some of the seven "swing states" I mentioned would have gone for McClellan if Atlanta had not fallen--but not all. In particular, I do not think that after Sheridan's victories McClellan would have carried Illinois, where Lincoln's OTL victory margin (54.4-45.6) was fairly comfortable; where the Republicans won a majority of the vote in most elections from 1858 until the New Deal; and where Lincoln would have a home-state advantage (which he didn't really have in 1860 because his main competitor for the state's electoral vote, Douglas, was also an Illinoisan). (It is true that Illinois voters did elect a Democratic legislature in 1862 but they already seem to have shifted their opinions by mid-1863, when the proposed "Copperhead Constitution" was defeated.) And without Illinois, McClellan IMO cannot plausibly win.
Now if Atlanta had not fallen *and* Sheridan had been defeated at Cedar Creek...
https://groups.google.com/d/msg/soc.history.what-if/lhaK6kHvIWs/fZctLnZ6d0QJ
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Also see
https://www.washingtonpost.com/news...lns-reelection-game-changer-or-campaign-myth/ "If Lincoln was in trouble before Atlanta, Republican vote share before September 1864 should appear lower than after. But if we see little change in Republican votes over time, it may suggest that Lincoln was on his way to reelection without Atlanta....
"... the midterm dip in 1862 looks more like a pattern quite familiar to us today: the tendency of the president’s party to suffer losses in the midterm.
"Notably, even at this lowest level of support, Republicans averaged only 3 percent worse than Lincoln’s 1864 vote share, short of the 5 percent threshold needed for Lincoln to lose in 1864. And by the fall 1863, Republicans fared substantially better, equaling or exceeding Lincoln’s 1864 vote share. The early 1864 elections also went well for Republicans. This suggests that Republican fortunes before Sherman reclaimed Atlanta were not actually that bad.
"Most important is the continuity between the elections before and after the fall of Atlanta. Republican vote shares in House and gubernatorial elections did not change that much. The Atlanta thesis should show Republican gains after the victory. The evidence shows otherwise..."