Any of these things happen in the time interval from the title:

• A constitutional amendment is passed and adopted

• There is an emergency presidential succession. IE vp or someone else suddenly becomes president outside of the normal schedule

• A nuclear weapon explodes in the USA of at least 50 kilotons

• A disaster strikes killing at least 10k people. Diseases count, quakes, volcanos etc. Manmade and natural

• An attack by a terrorist or nation or individual kills at least 3k people in the usa

• $collapse means the inflation rate is greater than 100% annualized for at least a month

• The mainland USA is invaded by a foreign power

• The US military suffers over 5000 casualties in a single incident (battle/attack/etc)

• The S&P decreases in value by over 80% in that month