Any of these things happen in the time interval and region in 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 suddenly (within 24h). Quakes, volcanoes etc. This includes both intentional and accidental manmade disasters as well as natural ones.
An attack by a terrorist or nation or individual kills at least 3k people in the usa
The inflation rate is greater than 100% annualized for at least a month
The US stock market is closed for at least 3 days consecutive which would normally be operating
Any of x.com, facebook, google, amazon is "down" or nonfunctional for at least 48 hours over the entire nation (>95% of the population) (can't post on x, can't search on goog, can't buy things on amazon)