Here's What Happens When The US Government Shuts Down On Oct 1 And How Markets Will React

While US government shutdowns have become so common in recent decades that every federal agency has a playbook for how to implement them, the Trump administration is rewriting those plans in advance of the end of the fiscal year this Tuesday, making a potential shutdown on Oct 1 even more unpredictable, and potentially disruptive, than any other in memory. 

Government shutdowns all have the same cause: Congress fails to approve new spending when previous spending bills expire. But their impact can vary based on timing, duration and quirks of the budget process that can make money available to some agencies but not others.