A look at which services may or may not be affected in a shutdown:
Federal air traffic controllers, airport screeners and federal inspectors would stay on the job.
The State Department would process foreign applications for visas and U.S. applications for passports. Embassies and consulates overseas would provide services to U.S. citizens.
Social Security and Medicare benefits would keep coming, but there could be delays in processing new disability applications. Unemployment benefits would still go out.
Federal courts would continue operating normally for about 10 business days. After that, the judiciary would have to begin furloughs of some employees, but cases would continue to be heard.
Deliveries would continue.
All national parks would be closed, as would the Smithsonian museums, including the National Zoo in Washington. Visitors using overnight campgrounds or other park facilities would be given 48 hours to make alternate arrangements. Among the centers that would be closed: the Statue of Liberty and Ellis Island in New York, Independence Hall in Philadelphia, Alcatraz Island near San Francisco and the Washington Monument.
New patients would not be accepted into research at the National Institutes of Health, but current patients would receive care. The Centers for Disease Control and Prevention would be limited in spotting or investigating outbreaks.
Federal meat inspections would be expected to proceed.