Under the Constitution, Congress must pass laws to spend money. If Congress can’t agree on a spending bill the government does not have the legal authority to spend money. Since the government runs on a fiscal year from October 1 to September 30, the spending authorization ends today. The Republican-controlled House passed a continuing resolution on September 20 that would have kept the government running until mid-December but would have cut funding to implement the Affordable Care Act (aka Obamacare). The Democratic-majority Senate rejected that plan and last week approved its own continuing resolution that included money for Obamacare.
The entire government doesn’t actually shut down during a government shutdown, does it?
No. Programs deemed “essential” — which includes, among other agencies and services, the military, air traffic control, food inspections, etc. — would continue as normal. “Non-essential” programs and services such as national parks and federal museums would be closed. Federal workers deemed non-essential will also be furloughed.
What about government benefit checks?