Friday marks the 21st day of the federal government shutdown — a tie for the longest in U.S. history.

It also marks a day that many of the thousands of federal workers will go without their latest paychecks, including those who rely on every check for basic necessities.

The impasse between Congress and President Donald Trump over his call for $5.7 billion to build a wall along the U.S.-Mexico border shows no sign of abating. As federal workers and contractors, state and local governments, and members of Congress call for an end to the partial government shutdown, the Trump administration on Thursday made preparations to declare a national emergency in order to receive the funding for the wall.

The effects of the shutdown continue to grow, and will only worsen as it goes on. The impacts could ripple through the entire economy.

FBI agents are warning of delayed investigations. Foreign embassies might have to close. An already deep backlog of immigration cases would grow deeper. Travel clearances could be delayed for refugees already approved to live in this country. People could run out of federal food assistance benefits. Environmental Protection Agency employees say the shutdown threatens public health and safety. Shutdown-related furloughs would cut into sales and income-tax revenue in Pennsylvania and New Jersey.

And Philadelphia tourism could take a hit. Last year, more than four million people visited Independence National Historical Park, which is closed during the shutdown.

Here’s some of what could happen if the shutdown continues indefinitely.

Economic repercussions: Home buyers scared away

The shutdown’s largest long-term impact could likely be its effect on consumer sentiment and economic outlook, said Mark Zandi, chief economist at Moody’s Analytics.

“I think with each passing week, the damage to the housing market and broader economy mounts,” Zandi said. “Particularly if this conflates with the Treasury debt limit later in the year and the budget for fiscal year 2020, which starts in October. If it all starts running together, then I think the issues for the housing market and the economy become much more serious.”

In a survey issued this week by the National Association of Realtors, 11 percent of the 2,211 real estate agents nationwide who were asked said that the shutdown had had an impact on their current clients. An additional 11 percent reported an impact on potential clients.

According to the association’s findings, 25 percent of Realtors who reported an impact said that their clients decided not to buy due to general economic uncertainty. An additional 9 percent of Realtors had clients who walked away from a purchase because they were federal employees. Three percent of Realtors who reported an impact said they had a buyer who was unable to buy due to lender rejection because of that person’s furlough.

Among those impacted, 17 percent had a delay because of a USDA loan, 13 percent experienced a delay due to IRS income verification, and 9 percent had a delay due to FHA loans. In some cases, the association found, the shutdown caused people to lose bids on their homes.

“This will start to undermine what has been close to record levels of consumer confidence,” Zandi said. “Housing is very vulnerable to that. You only make a housing purchase if you are very confident.”

With a national slowdown already occurring in the housing market, evaporating confidence could be a problem when the market gets hot in the spring.

“If they don’t resolve this thing in the next month, I think the key housing selling season is in jeopardy,” Zandi said.

Last week, the Philadelphia Housing Authority said contingency funding was available to float operations for at least two months. It was unclear what could happen after that. — Caitlin McCabe

Food stamps coming, but so will confusion?

While the 1.8 million Pennsylvanians who receive food stamps under the Supplemental Nutrition Assistance Program will get benefits at least through the end of February, advocates see the potential for problems. The federal government announced its protection plan this week, amid growing concern that the U.S. Department of Agriculture, one of the agencies affected by the shutdown, might not be able to get the benefit to 42 million Americans.

The USDA’s funding expired on Dec. 21, but Pennsylvania and other states had already received money to pay January benefits.

To keep the program alive in February, though, states will need to issue the benefits by Jan. 20, the agency said. That means Philadelphia’s 480,000 recipients will get their February money added to their accounts early.

Kathy Fisher, policy director of the Greater Philadelphia Coalition Against Hunger, said there’s some concern that people will unknowingly spend those February benefits early.

“We are really worried that it could be very confusing,” Fisher said. “Not everyone receiving SNAP is following all the details of the shutdown. Even if they can issue a letter to all 1.8 million SNAP recipients in the state, we don’t know everyone routinely gets their mail. If their SNAP card suddenly has money on it and they need to eat, they don’t necessarily know that’s their February benefit. Are they going to run out of food?”

Fisher also said retailers who accept electronic benefit payments, which typically slow by month’s end, could see a spike in January. Food pantries could see more demand in February, she said, if people run out.

The Department of Agriculture has provided no plan for what happens to the benefits in March.

School lunch programs will be funded through March and WIC (Women, Infants, and Children Food and Nutrition Service) will continue at least through February, the agency has said.

The shutdown has not affected other public benefits, like Temporary Assistance for Needy Families (TANF), Social Security, Medicaid, and Medicare. There’s no sign that will change any time soon, said David Hill of the Legal Assistance Center.

“We would be getting warnings,” he said. “If there were any kind of major announcement, then there would be doomsday signals, but there’s been nothing like that so far.” — Julia Terruso

Immigration, visa, and refugee systems will stall

Nobody is quite sure what happens to the nation’s immigration system if the shutdown goes on indefinitely, but everyone connected to the system is deeply concerned about it.

An extended shutdown will continue to bloat the backlog of deportation cases in immigration courts, as hundreds of hearings a day are canceled to await rescheduling, predicts Philadelphia immigration attorney William Stock, past president of the national chapter of the American Immigration Lawyers Association.

Eventually, Stock said, a lengthy shutdown will close the nation’s overseas embassies.

The State Department has been using certain multiyear appropriations to keep embassies open. but eventually that money will run out and embassies will become “emergency only” operations.

“When that happens, no one will be able to get visas to come to the U.S. and do business, or attend school next fall, or be tourists, which will harm the economy," Stock said.

Margaret O’Sullivan, executive director of Nationalities Service Center, the resettlement agency in Philadelphia, worries that a protracted shutdown will dramatically slow the processing for refugees already approved to come to the United States but still awaiting travel clearance.

"An extended shutdown could completely shatter the chances for refugees fleeing unspeakably tragic circumstances to make their way here,” she said, “where they hope to build a better life for their families and contribute to our community and economy.”

The E-Verify system, designed to prevent migrants from working illegally in this country, has ceased operation during the shutdown. — Jeff Gammage

Delays at the FBI

On Thursday, the union that represents thousands of FBI agents said the shutdown may hinder the bureau’s operations. The shutdown could delay lab results and security clearances, and make recruiting and retaining agents more difficult, according to the union. — Michaelle Bond