With Donald Trump, the most extreme and unqualified candidate of a major party, in striking distance of winning the presidency, we stand on the edge of the abyss. This election shouldn't be this close. You can use the comments section as an open thread as the next few days unspool. For my contribution, here are a dozen of the most consequential elections, nationally and in Arizona. At the least, they show that elections do indeed matter.
1828: John Quincy Adams vs. Andrew Jackson. Adams, the sitting Whig president, was defeated by war hero Jackson. The Whigs stood for the "American System" of internal improvements (infrastructure), a national bank and limiting the spread of slavery. Jackson was just the opposite. Jackson's victory led to the breaking of solemn treaties with the Five Civilized Tribes and their brutal relocation west (denounced by Adams) to open land for slaveholders, among many other ills.
1844: James K. Polk vs. Henry Clay. The defeat of "Harry of the West" not only doomed the American System but eliminated the last chance that the Civil War might have been postponed or avoided. One reason was the familiar partisan circular firing squad. Clay lost votes in New York and Pennsylvania to the abolitionist Liberty Party. It was the death of the Whigs.
With Polk, the nation again had a Southerner determined to extend slavery, including by prosecuting the highly unpopular Mexican War. At one point, Polk considered demanding all the territory to Tampico, but didn't want so many Mexicans brought into the union (they automatically became U.S. citizens with the Treaty of Guadalupe Hidalgo, which ended the war). On the other hand, in settling the Oregon Country dispute with Great Britain, he would have settled for the Columbia River as the northern border (in other words, Seattle would be in British Columbia). With Polk, the Civil War became inevitable.