The last such shutdown took place 15 years ago and lasted 21 days.
Under long-standing federal rules, agencies would not be affected that provide for U.S. national security, dispense most types of federal benefit payments, offer inpatient medical care or outpatient emergency care, ensure the safe use of food and drugs, manage air traffic, protect and monitor borders and coastlines, guard prisoners, conduct criminal investigations and law enforcement, oversee power distribution and oversee banks.
Mail deliveries will continue in the event of a shutdown. U.S. postal operations are not subsidized by tax dollars.
According to the shutdown scenario described by the administration, the government would have to significantly cut staffing across the executive branch, including workers at the White House and civilian employees at the Defense Department; close to 800,000 workers would be affected. Congress and the federal court system will also be subject to a shutdown.
At the Pentagon, defense officials were finalizing plans that would lay out how the department would deal with a shutdown. But they already have acknowledged that U.S. military troops - including those in war zones - would receive one-week's pay instead of two in their next paycheck if the government closes.