We're already seeing the effects of the government shutdown. More than 700,000 federal workers have been sent home without pay. National parks and memorials are barricaded. The National Institutes of Health is turning away cancer patients from clinical trials.

Congress’s spending impasse shuts down the national parks. (Someone tell Smokey Bear.) (Steve Helber/Associated Press)

But when do these effects become so overwhelming that the political pressure on Congress becomes unbearable? How long can members of Congress hold out before they simply have to reach a deal and end the shutdown?

That's a harder question, and there's reason to think that Congress can hold out for quite some time — a week, perhaps more. During the last shutdown in 1995-96, only a small portion of the country felt the impacts at first. It wasn't until contractors and businesses started laying people off that the political pressure became more acute. That could take awhile.

On the flip side, however, the shutdown will become increasingly painful and politically volatile as it drags on. If the impasse extends past the middle of the month, millions of paychecks will get delayed and veterans' benefits could get disrupted. So it's not clear Congress and the White House can hold out forever, either.

The politics of the shutdown


It's worth noting that some politicians are already feeling pressure from the shutdown. As of Thursday, 19 Republicans in the House have come out in favor of a "clean" continuing resolution that would fund the government without demanding changes to Obamacare — a position Democrats have said they would accept.

Four of those Republicans in favor of ending the shutdown hail from Virginia, which has 144,573 federal workers, the second-most of any state in the country. Four other Republicans come from Pennsylvania, which ranks seventh on the list.

But it's unlikely that the furloughs of 770,000 federal workers alone will sway Congress — after all, lawmakers have felt little urgency to resolve the sequestration budget cuts, which have also sent thousands of federal workers home without pay. That's why many observers think we'll have to wait until the shutdown affects a broad swath of middle-class Americans.

"It's when you start getting Republican-type folks who are directly affected," says Vin Weber, a lobbyist and former Republican Congressman. "People who are trying to get a small-business loan and can't get processed. Then [Republicans in Congress] will start getting a very different message than what they have been hearing the last few months, when they've only heard from people arguing in favor of a shutdown.

Still, it's fair to ask how many middle-class Americans will actually be squeezed. During the 1995-'96 shutdown, polls found that just 12 percent of respondents said they were personally inconvenienced, with only 4 to 6 percent saying it was a major inconvenience.

That's why we may have to wait until major businesses and contractors are affected, says Stan Collender, a budget expert at Qorvis communications.

“If you look at the last shutdown,” Collender told me, “what happened after about a week was that anyone who did business with the government — contractors, subcontractors — realized this is really hurting. Contractors started announcing they were going to lay off people. And that’s when it turned real. There wasn’t a market reaction — there was a business reaction.”

And right now, many federal contractors simply don't know how their businesses will be affected. It's a sizable market. In 2012, military contractors did about $1 billion worth of business each day with the Department of Defense — and many of those contracts are likely to be put on hold. It's just unclear how many. "We still don’t know exactly how many contracts count as 'essential' services," says Rob Levinson, a senior defense analyst at Bloomberg Government.

Partly because this is still getting sorted out, Collender has argued that the shutdown could last a week or more.

Hard deadlines will start to emerge

(The Washington Post)

If the shutdown goes on for more than two weeks, however, Congress will start bumping up against a bunch of other politically volatile deadlines:

Paychecks for essential workers. There are currently 1.3 million government workers who are continuing to perform "essential" government duties, from air-traffic control to hospital care. These workers are all entitled to pay and got their last paycheck on Oct. 1 or Oct. 3.

However, if the shutdown extends past Oct. 11, then many of these workers won't get their next paycheck right away — it will be delayed. Suddenly, the shutdown will affect the pay of millions more people. (There are exceptions for the 1.4 million active-duty military, who will be paid regardless.)

Veterans. The Department of Veterans Affairs has told lawmakers that it will run out of money to pay disability claims or make pension payments for up to 3.6 million veterans if the shutdown lasts for more than two or three weeks.

School closings. Other programs will continue to wither over time if the shutdown is prolonged. A handful of Head Start programs for some 3,200 pre-schoolers have already closed because their grants have expired. Even more schools will close as the shutdown continues, affecting thousands more kids.

Clinics closing. Many state Women, Infants, and Children programs that provide nutrition will also start running out of money if the shutdown goes on for more than a week, the U.S. Department of Agriculture has warned. (It varies state to state, depending on their reserve funds.) Some nutrition clinics are already closing in states like Utah.

That said, it's unclear if even these stories will sway a critical mass in Congress: "One sad reflection here is that the stories about the most vulnerable population might not be the impacts that loom largest," says Weber. "The ones that will make the most political impact are when you really start annoying middle-class people pursuing their lives."

And the really hard deadline: The debt ceiling

The range of dates when the government could start defaulting on the bills it owes. (Bipartisan Policy Center)

Finally, there's the biggest deadline of all: The debt ceiling. By Oct. 17, the Treasury Department will only have about $30 billion in cash to pay its bills — and it won't be able to borrow any more money unless Congress lifts the debt ceiling. (This date is unlikely to be affected much by the shutdown, Treasury says.)

That's a potential problem, because, come Nov. 1, the Treasury has to make about $42 billion worth of Medicare and Social Security payments. If the government is barred from borrowing money, it won't have enough cash to pay that bill. The betting at this point is that Congress wouldn't possibly allow the government to default on Social Security and Medicare.

At least, that's the theory. But already there's sharp disagreement here. Some Republicans have suggested that a big budget deal could resolve both the shutdown and the debt-limit clash. But Democrats argue that the debt ceiling should be raised without any conditions at all. So it's tough to say just how absolute this deadline really is.

Related: Absolutely everything you need to know about how the government shutdown will work