This past election cycle has featured the usual array of punditry about allegedly game-changing campaign events. Perhaps if some Democratic candidates had been more embracing of President Obama, or mounted a more forceful defense of the economy or health care reform, or not gambled everything on a campaign about abortion rights, they might have done better. Perhaps if Obama had pushed his executive action on immigration back in September rather than November, Democratic turnout among Latinos might have been higher. Et cetera.
What turned the tide for Lincoln—and indeed, for the Union's war efforts—was General Sherman's extremely audacious plan to split the Confederacy and decimate its economy.
Chances are, few of these events would have made an enormous difference in the outcome of the election. Given the map of 2014, the state of income growth, and the popularity of the president, Democrats would likely have lost the Senate regardless, and pundits would now be saying the precise opposite. (Why didn't Obama wait until after the election to deal with immigration?)
For an example of an actual election game-changer, check out historian Susan Schulten's recent post on General Sherman's March to the Sea in 1864 and its impact on President Lincoln's re-election campaign that year. As Schulten notes, Lincoln's re-election was far from certain up until relatively late in that campaign:
Lincoln himself faced criticism on all sides: many anti-war Democrats insisted he was a tyrant who cavalierly imposed a draft and violated civil liberties, while his fellow Republicans charged that he was insufficiently prosecuting the war against the Confederacy. The big gains of 1863—Gettysburg and Vicksburg—began to seem like distant memories. The party even flirted with the idea of dumping Lincoln for another candidate, and a pesky third-party candidate, John Fremont, threatened to steal away the votes of unsatisfied Republicans. ... That grim summer, Lincoln actually acknowledged that he might lose the election.
What turned the tide for Lincoln—and indeed, for the Union's war efforts—was General Sherman's extremely audacious plan to split the Confederacy and decimate its economy. Schulten explains a bit of this plan's audacity here, noting that it involved moving three entire armies from northwestern Georgia into Atlanta, then to Savannah, and then north into the Carolinas, all beyond Union supply lines. Sherman made extensive use of mapping to allow his armies to live off of the land while conducting this campaign, essentially knowing the terrain better than the local armies they were fighting. Sherman took Atlanta on September 1, marking a major turn for the Union just at the beginning of the political campaign season.
It's of course difficult to get a sense of the political fundamentals from 1864. But from what we know, it looks like per capita GDP actually shrank between 1863 and 1864, and inflation was very high that year. Yet there was not as much of a sense of a national economy in the mid-1800s as there is today, and the federal government wasn't seen as having much responsibility for its success or failure. To the extent we can tell, though, Lincoln faced a legitimate chance of losing that year; two-term presidencies were still pretty rare at that point, and the event most closely identified with his presidency had not been going particularly well until pretty late in the game.
Sherman's successes that summer and fall may well have saved Lincoln's presidency. And they give us an idea of just what an electoral game changer actually looks like. An army seizing a major city in rebellion, not a particular advertisement or speech, is the sort of thing it takes to tip an election.