In less than three weeks the federal government could partially shut down if Congress doesn’t act. So, what would that look like?

If past is prologue, national parks and the National Zoo would be shuttered; many federal employees would be furloughed; and food inspections would be delayed.

But if the most recent shutdown — in 2013 — is an indication, unemployment-benefit checks will go out, and Americans will keep getting their mail delivered through the U.S. Postal Service. A USPS spokesperson confirmed delivery would not be affected since the postal service relies on income from stamps and other fees to keep running, and doesn’t depend on the congressional appropriations process.

Washington is staring down a Sept. 30 deadline to keep the government open, and right now, there’s no resolution in sight. On Thursday, House Speaker John Boehner said it’s not “his goal” to shut down the government over the issue of funding Planned Parenthood. Some conservatives want to cut off federal dollars for the provider of women’s reproductive health services.

Also on Thursday, White House press secretary Josh Earnest urged Republicans to start budget negotiations with Democrats. The White House wants Congress to lift spending caps for domestic spending, not just for the military.

Earnest said there is a “regular process” for federal agencies to prepare for a shutdown but added he did not know if those had begun or not. A MarketWatch request for more information from the Office of Management and Budget was not immediately answered.

Congress hasn’t passed a single spending bill for the fiscal year that begins Oct. 1.

The last time the government shut down was Oct. 1-16, 2013, after a fight over Obamacare. About 850,000 federal employees were furloughed immediately after funding ran out, according to a White House report. But most civilian employees of the Defense Department went back to work after a week, following passage of the Pay Our Military Act. More than 8,000 workers at the Social Security Administration were recalled as well, to ensure benefits were processed.

Budget expert Stan Collender of Qorvis MSLGroup points out presidents have the authority to determine which activities will continue during a shutdown.

“There’s no agreed-upon list of what’s essential and what’s not, and the president can (and typically does) change the list as a shutdown continues,” Collender told MarketWatch in an email.

While there’s flexibility in terms of what can stay open and what shuts down, the last two shutdowns have claimed some of the same victims. In both 1996 and 2013, for example, the Smithsonian museums in Washington were closed. Employees were furloughed, though paid later.

Alec Phillips of Goldman Sachs says he doesn’t expect another shutdown to look much different from prior ones — if it comes to that.

“With a few weeks to go until the deadline, the outlook is very murky but our best guess is that Congress will narrowly avoid it,” he wrote in a note on Wednesday.

There could be more clarity early next week on where this issue is going. Politico reports House Republican leadership aides have said they will decide on a strategy to fund the government by the end of this weekend.