Economist Martin Armstrong's blog:

If we look at the timing from Dred Scott decision, the war began when the Confederates bombarded Union soldiers at Fort Sumter, South Carolina on April 12, 1861, which was 4.1 years or almost the half-cycle point of 4.3 years. The war ended officially in the Spring of 1865. Robert E. Lee surrendered the last major Confederate army to Ulysses S. Grant at Appomattox Courthouse on April 9th, 1865. However, it was the Shenandoah surrender on November 6th, 1865 that marked the final military activity.

Therefore, if look at that timing, it would appear that 4.3 years from Trump swearing in on January 20th, 2017 brings us to 2021.354. If we throw in all the economic problems we see coming with pensions and a monetary crisis on top of all of that, I would not count of 2020 being a normal presidential election. It may be the most violent event in American political history.