I searched previous US inauguration charts to find similarities to 2021. Previous times that a US President was inaugurated when Mars was in Taurus include 1797 (Adams), 1829 (Jackson 1st), 1893 (Cleveland 2nd), 1925 (Coolidge 2nd), 1989 (HW Bush) and...1861 (Lincoln 1st).

What makes 1861 stand out from the others is that Mars is not just by itself, it's in early Taurus conjunct an outer planet, Pluto. Similarly at the 2021 inauguration, Mars is in early Taurus, conjunct an outer planet, Uranus. Here is Wikipedia on the 1861 inauguration:

"On Inauguration Day, Lincoln's procession to the Capitol was surrounded by heavily armed cavalry and infantry, providing an unprecedented amount of protection for the President-elect as the nation stood on the brink of war...

...During the 16 weeks between Lincoln's victory in the 1860 presidential election and Inauguration Day, seven slave states had declared their secession from the Union and formed the Confederate States of America."

Sound even vaguely familiar?

I tried to find another inauguration with Mars conjunct Uranus. There are none, it was only 1909 (Taft) and 1965 (LBJ) that they're even copresent at all. The one with the closest copresence of Mars and Uranus was...1865 (Lincoln 2nd). He was murdered less than 2 months after.

To be clear, I am NOT predicting that Biden will be assassinated or something. According to his Spirit ZR, I see him declining to run for a 2nd term after April 19th 2023, as the Loosed repetition of his decision not to run in 2016. https://patrickwatsonastrology.com/joe-bidens-zodiacal-releasing-and-the-2020-us-presidential-election/

However, I do think the Mars connections between the 2021 inauguration and 1861/1865 inaugurations show the presidency facing down similar foes and challenges.