The sting of government operations going unfunded would be felt deeply by some, but other government entities would continue business as usual.
The details of a shutdown are left to the executive branch of government and the Office of Management and Budget has so far not provided any details. But based on past shutdowns, here are some guidelines on what could happen:
Federal air traffic controllers would likely remain on the job and airport screeners would keep funneling passengers through security checkpoints. Federal inspectors would continue enforcing safety rules.
Social Security and Medicare benefits would keep coming, but there could be delays in processing new disability applications. Unemployment benefits would still go out.
Deliveries would continue as usual because the U.S. Postal Service receives no tax dollars for day-to-day operations. It relies on income from stamps and other postal fees to keep running.
New patients would not be accepted into clinical research at the National Institutes of Health, but current patients would continue to receive care. Medical research at the NIH would be disrupted and some studies would be delayed. The Centers for Disease Control and Prevention would be severely limited in spotting or investigating disease outbreaks, from flu to that mysterious MERS virus from the Middle East.
A small number of Head Start programs, about 20 out of 1,600 nationally, would feel the impact right away. The federal Administration for Children and Families says grants expiring about Oct. 1 would not be renewed. Over time more programs would be affected. Several of the Head Start programs that would immediately feel the pinch are in Florida. It's unclear if they would continue serving children.
The Special Supplemental Nutrition Program for Women, Infants and Children, known as WIC, could shut down. The program provides supplemental food, health care referrals and nutrition education for pregnant women, mothers and their children.
School lunches and breakfasts would continue to be served, and food stamps, known as the Supplemental Nutrition Assistance Program, or SNAP, would continue to be distributed. But several smaller feeding programs would not have the money to operate.
Americans would still have to pay their taxes and file federal tax returns, but the Internal Revenue Service says it would suspend all audits. Got questions? Sorry, the IRS says taxpayer services, including toll-free help lines, would be shut as well.
Many low-to-moderate incomes borrowers and first-time homebuyers seeking government-backed mortgages could face delays during the shutdown. The Federal Housing Administration, which guarantees about 30 percent of home mortgages, wouldn't underwrite or approve any new loans during the shutdown. Action on government-backed loans to small businesses would be suspended.
The majority of the Department of Homeland Security's employees are expected to stay on the job, including uniformed agents and officers at the country's borders and ports of entry, members of the Coast Guard, Transportation Security Administration officers, Secret Service personnel and other law enforcement agents and officers. U.S. Citizenship and Immigration Services employees would continue to process green card applications.
The military's 1.4 million active duty personnel would stay on duty, but their paychecks could be delayed. About half of the Defense Department's civilian employees could be furloughed. The House Saturday passed a measure that would ensure military personal would continue to be paid, something that is likely to pass the Senate even in the event of a shutdown.
See how the shutdown would affect other departments:
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