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

• A Kaiju attacks US territory resulting in at least 100 deaths. Any new large philysical monster or creature counts if it's "alive" and self-controlled