At least one-quarter of the government is affected as the partial government shutdown stretches into 2019 — and while federal employees are hit the hardest during this period, some closures impact the general public, too.

President Trump has been prodding top Democratic leaders to come to an agreement on a spending package, particularly in regards to funding for border security. On New Year's Day, Trump urged House Democratic leader Nancy Pelosi on Twitter to "start her tenure as Speaker" on the right foot.

"Let's make a deal?" he then asked.

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According to a precedent set during the Reagan administration, federal workers can be exempt from furloughs if their jobs are related to national security or if they perform essential activities that “protect life and property.”

Read on for a look at which agencies are open, which are closed and who still is expected at work during this time.

What's open and operating?

U.S. Post Office

The U.S. Postal Service (USPS) will remain open as usual during a partial government shutdown because it is “an independent entity that is funded through the sale of our products and services, and not by tax dollars,” a spokesman told Fox News. Passport services, which are funded by fees and not government spending, will also continue.

Essential government agencies

Virtually every essential government agency, including the FBI, the Border Patrol and the Coast Guard, remains open. Medicare, Medicaid, Social Security, veterans' health care and many other essential government programs are also running as usual.

While these agencies remain open, officials note that they still notice an impact on some operations. The Coast Guard, in particular, has said the shutdown has reduced boating safety checks, patrolling and mariner licensing, according to Politico.

“The longer the shutdown lasts, the more difficult it will become for the Coast Guard to maintain mission readiness,” Coast Guard spokesman Chad Saylor told the publication.

Federal courts

The federal judiciary will remain open at least until Jan. 11, the U.S. Courts said on its website. It will use court fee balances as well as additional funds that are “not dependent on a new appropriation” to stay open.

"Most proceedings and deadlines will occur as scheduled. In cases where an attorney from an Executive Branch agency is not working because of the shutdown, hearing and filing dates may be rescheduled," it stated online.

If the partial shutdown surpasses its three-week deadline, then the courts would operate under the Anti-Deficiency Act.

"Under this scenario, each court and federal defender’s office would determine the staffing resources necessary to support such work," according to the U.S. Courts.

Food stamps

The Supplemental Nutrition Assistance Program, or food stamps, helps feed roughly 40 million Americans. According to the USDA, eligible recipients are guaranteed benefits through January.

Other feeding programs, including WIC, which provides food aid and nutrition counseling for pregnant women, new mothers and children, and food distribution programs on Indian reservations, will continue on a local level, but additional federal funding won't be provided. School lunch programs will continue through February.

Military

Active duty military members are exempt from government shutdown furloughs, according to the Department of Homeland Security.

Mueller's Russia probe

Special counsel Robert Mueller's office, which is investigating potential ties between the Trump campaign and Russia, is unaffected by a shutdown.

Public transportation and security

TSA agents, air traffic controllers and border security agents also will be required to work through a shutdown – albeit they might not get a paycheck right away.

Amtrak, a government-owned corporation, also will continue with normal operations during a short-term shutdown, a spokeswoman confirmed to Fox News.

What's closed?

9 Cabinet-level departments

Nine of the 15 Cabinet-level departments — Agriculture, Commerce, Homeland Security, Housing and Urban Development, Interior, Justice, State, Transportation and Treasury — are without funding, meaning parts of their operations are shuttered.

Essential personnel are still required to work but without pay (nearly 90 percent of the Homeland Security staff is deemed essential).

EPA

The Environmental Protection Agency (EPA) warned employees that it would likely have to shutter on Jan. 1. The agency now lists a warning online stating EPA websites will not be "regularly operated" due to a "lapse in appropriations."

IRS

The start of tax season may be postponed as the International Revenue Service (IRS) has furloughed roughly seven in eight workers, according to Politico. During this time, the IRS will process tax payments, but returns will be delayed, Fortune notes.

National museums and more

On Jan. 2, the Smithsonian announced it had to close at least 19 Smithsonian museums and the National Zoo in Washington, D.C. If the shutdown continues, many popular museums and art galleries are likely to follow suit as they exhaust temporary unspent funds.

The National Gallery of Art in Washington, D.C., is also slated to close on Jan. 3, WTOP reports.

Who has to work without pay?

More than 420,000 people — including law enforcement and Homeland Security workers — have had to work with their pay withheld, according to Senate Democrats.

About 53,000 TSA employees, 54,000 Customs and Border Protection agents and 42,000 Coast Guard workers are required to work without pay.

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Additionally, about 5,000 Forest Service firefighters need to work, according to Senate Democrats.

Who is furloughed?

More than 380,000 people are furloughed in the shutdown — meaning they will experience a temporary leave from their work.

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This will include most of NASA, Department of Housing and Urban Development, Commerce Department and National Park Service workers. Additionally, about 52,000 IRS workers are furloughed.

Fox News' Jennifer Earl and The Associated Press contributed to this report.