Scenarios
Sam Cedar creates a new drug called Cedardone that is extremely expensive and addictive. Sam makes over a trillion dollars in sales in the first month which he puts in his personal vault and never buys anything or reinvests.
Income goes down and interest rate goes up. LM to the left. IS stays the same.
A typo in the government system caused income tax to be 100% instead of 10%. Unfortunately, the entire server room burned down the same day, meaning it will take at least a month to reverse the error. Instead, the government sells $100 billion in treasury bonds to offset the error.
R down, income inconclusive (but likely down). IS left, LM right.
The USA joins with Canada and Mexico into one super-continent. The USD is the currency for all three.
The current interest rate is 0%. The Fed decides to buy $1 billion in bonds while also increasing spending on Medicare by $1 billion.
Interest rate remains at 0%, income down. LM right, IS left.
After the US Air Force purchases 300 F-22 fighter jets to combat an alien invasion of the Moon, a minor increase in taxes is passed in an offsetting effort. Meanwhile, a self-aware computer virus called Skynet doubles all money in US checking accounts, with an intent to cause chaos but it instead benefits the American people.
Interest rate is inconclusive, and income is also inconclusive. IS goes left at first but then shifts right, LM right.