1. Inauguration Day: January 20 is significant in Washington DC history as it marks the day of presidential inaugurations. Since the enactment of the 20th Amendment in 1933, the President of the United States has been inaugurated on January 20, or on January 21 if January 20 falls on a Sunday.

2. Martin Luther King Jr. Day: January 20 is also a federal holiday in honor of civil rights leader Dr. Martin Luther King Jr. King's birthday was designated as a federal holiday in 1983 and first observed on January 20, 1986. On this day, many Washingtonians attend commemorative events and service projects in honor of King's legacy.

3. Women’s March: One of the largest protests in Washington DC history took place on January 20, 2017, when an estimated 500,000 people marched in the Women’s March on Washington. The demonstration was organized in response to the election of Donald Trump as President and called for equality and women's rights.

4. First Presidential Ball: The first inaugural ball in Washington DC took place on January 20, 1809, for President James Madison. The tradition of an inaugural ball continues to this day, with multiple events hosted throughout the city on Inauguration Day.

5. Bloodless Transfer of Power: On January 20, 1981, Ronald Reagan became president, marking the first time an inauguration ceremony was held on the West Front of the U.S. Capitol. The ceremony also included a symbolic moment in which outgoing President Jimmy Carter and incoming President Reagan drank a toast to the peaceful transfer of power. This tradition continues today.