At the National Zoo in Washington, the animals would still be fed and cared for. But while final arrangements haven't been determined, it's possible that waste removal services would be cut off temporarily.
Will members of Congress be affected?
Congress is considered an essential government function, so members of Congress and their staffs would be paid and would report to work as usual -- even though it would be their inaction leaving so many federal workers idling.
The same goes for White House and top administration staff. But some services would be affected; during the last shutdown, for instance, the presidential limousine famously went to a public car wash, because those who usually serviced the vehicle were furloughed.
What are the politics of a shutdown?
Political analysts generally agree that the two partial shutdowns that occurred in late 1995 through early 1996 were a net negative for congressional leadership, who appeared to shoulder much of the political blame for a situation the public viewed as senseless.
Then, as now, the standoff pitted a Democratic president against a new Republican majority on Capitol Hill that was committed to reining in government spending.
Intriguingly, the man perhaps held most responsible for the last shutdown -- then-House Speaker Newt Gingrich -- now argues that the stand-off was a net positive for the GOP, as it contributed to the balanced budgets achieved later in the decade.
Gingrich writes in a Washington Post op-ed published today that while a shutdown "is not an ideal result," it "would be far worse" for Republicans to break their word when it comes to cutting spending.
It's not clear, however, that the current House speaker sees things the same way. In a speech to be delivered today, Speaker John Boehner said that while Congress has a "moral responsibility" to cut spending, he recognizes that the public does not want government to shut down.
"This is very simple: Americans want the government to stay open, and they want it to spend less money," said Boehner, R-Ohio. "We don't need to shut down the government to accomplish that. We just need to do what the American people are asking of us."