The Democratic Party of James Buchanan, from 1855-1860, appeared ― on the surface ― to be ascendant in the American politics of the day. They controlled the presidency, majorities in the Congress and the majority of state legislatures and governorships. Their great rival party, the Whigs, had collapsed into internal factions after their 1856 electoral loss and the new Republican Party was nascent. They were so powerful that they controlled both the entire south and significant parts of the North ― and there was, of course, no “west coast blue wall” in the 1850s.

Nonetheless, the supposed dominance of the Democratic Party in the late 1850s papered over and masked critical internal divisions that would destroy the party in 1860 and leave it nearly irrelevant at the presidential level for almost 70 years.

Basically, those critical internal divisions were between the Southern Democrats, who were unified behind slavery and “southern values” and the Northern Democrats, who were much warier of slavery and were much more unified around economic concerns. Their uneasy alliance collapsed entirely in 1860, when the party actually split on the ballot between the Northern and Southern Democrats, handing Lincoln the election. The south seceded, Lincoln won the Civil War and the party didn’t recover until FDR. Indeed, the collapse of the party was so catastrophic that the only times the Democrats won the presidential election between 1856 and 1932 were typo non-contiguous terms for the idiosyncratic Grover Cleveland, and when Teddy Roosevelt split the Republican vote off Taft in 1912 and threw the election to Woodrow Wilson.

History repeats itself in inexact cycles, and the Republican Party of today bears remarkable similarities to the Democratic Party of the 1850s.

The most compelling comparison is the split today between Southern Republicans and their unsettled allies in the Midwest and various blue enclaves across the U.S. Since Richard Nixon and Ronald Reagan, the Republican Party has maintained an alliance between its business side of the party, which wins elections in upper crust house seats in suburbs across the country, and its evangelical, white supremacist wing, which dominates the South. What the 2017 elections showed is that alliance is collapsing: Republicans in high-income, high-education, traditionally GOP areas lost en masse because the GOP has become too toxically associated with white supremacy and the culture wars for locals’ taste.

Those Democratic wave results look like they may accelerate the collapse in the wary alliance between these two sects of the GOP. The biggest clue will be a wave of retirements (which is already ongoing, and may accelerate) for Republicans in traditionally red suburban seats in blue states. If the Democrats can win those seats en masse ― as they did overwhelmingly in the Virginia House of Delegates ― in 2018, then they will essentially cut one arm off the GOP.

In turn, this could accelerate a GOP civil war in 2020. The reason would be that the loss of those moderate conservative seats would further slant the GOP toward its southern primary voters, and the white supremacist nativism at the heart of Trumpian politics. This would, in its turn, turn off suburban voters in Michigan, Pennsylvania, Wisconsin, Florida, Arizona and North Carolina ― the states that hold the key to the presidential election ― effectively splitting the party much as the Northern Democrats split from the southern in 1860, and throw the election to the Progressive Democrats.

If that happens, hopefully this time we can avoid a repeat of the next period of American history, the Civil War.