• Congress had until midnight Friday to either pass spending bills for seven federal agencies or approve a stopgap spending measure that would push off a shutdown by a few months.
  • After those failed efforts, hundreds of thousands of American jobs will be directly affected in the heart of the holidays.
  • Trump wants $5 billion in funding for the construction of a wall along the U.S.-Mexico border and has said he would be "proud" to shut the government down if Congress doesn't accede to his demand.

A partial government shutdown began early Saturday after President Donald Trump dug in his heels on his demand to fund a border wall.

Congress had until midnight Friday to either pass spending bills for seven federal agencies, or approve a stopgap spending measure that would push off a potential shutdown. After those efforts failed, the closure will affect hundreds of thousands of Americans' jobs through the holidays.

Trump wants $5 billion in funding to build a wall along the U.S.-Mexico border, and said he would be "proud" to shut the government down if Congress doesn't accede to his demand.

The Office of Management and Budget started notifying federal agencies Thursday that they should prepare for a shutdown. Yet since lawmakers have already funded large portions of the government through the 2019 fiscal year, the current crisis would only shut down parts of the government. The unfunded agencies make up about a quarter of the government.

This is what was expected to happen during the shutdown, as of Friday:

Federal employees will work without pay

More than 420,000 federal employees across numerous agencies will continue to work even as the government shuts down. They just won't get paid for it immediately.

Democrats on the Senate Appropriations Committee said that number will include more than 41,000 federal law enforcement and correctional officers from the FBI, the Drug Enforcement Agency, the Bureau of Alcohol, Tobacco, Firearms and Explosives, and thousands of other law enforcement and correctional officers.

The vast majority of Department of Homeland Security employees will also work without a regular paycheck. The nearly 90 percent of workers in the agency affected by a shutdown would include 53,000 Transportation Security Administration employees, as well as 42,000 Coast Guard employees.

As many as 54,000 employees from Customs and Border Protection — the agents who are currently working to secure the southern U.S. border — were also projected to work without paychecks. By forcing a shutdown over border security, Trump was expected to cause the agents he often lauds for their efforts to stop illegal immigration to temporarily go without compensation.

Up to 5,000 Forest Service firefighters and 3,600 National Weather Service forecasters will also keep working without paychecks, according to Senate Democrats.

The special counsel's office, which is investigating potential criminal connections between the Trump campaign and the Kremlin, will continue operating.

Furloughed workers

Another 380,000 federal workers or more could be placed on temporary leave without receiving pay in the event of a government shutdown, according to the Democrats.

Furloughs will affect vast swathes of Department of Commerce and NASA staff. About 41,000 people, or 86 percent, could be furloughed from the Commerce Department, along with a staggering 96 percent of NASA employees.

Four-fifths of the Forest and National Park Services, totaling more than 44,000 employees, could be sidelined, as could approximately 52,000 staff from the IRS, and about 7,100 Housing and Urban Development workers — 95 percent of the total.

Thirty percent of Transportation Department employees, equaling about 18,300, could be furloughed, as well.

All of that lost work could cost taxpayers huge amounts of money. An Office of Management and Budget review of a 2013 government shutdown during the Obama administration concluded that the cost of "the lost productivity of furloughed workers" alone was $2 billion. The cost may not go that high this time, with five agencies still up and running.

That shutdown was one of the longest in U.S. history. The failure to fund the government by midnight Friday could create a closure that lasts into the new year, when Democrats take majority control of the House.

Trump himself said in a tweet Friday morning that "if the Dems vote no, there will be a shutdown that will last for a very long time."

Department closures

Nine federal departments will be shuttered as the government shuts down this weekend. They are:

  • Department of the Treasury
  • Department of Agriculture
  • Homeland Security Department
  • Department of the Interior
  • Department of State
  • Department of Housing and Urban Development
  • Department of Transportation
  • Department of Commerce
  • Department of Justice

"Dozens" of U.S. agencies will also close down during the shutdown, according to the report from the Senate Democrats. Those closures could lead non-federal employees to feel the impact of the shutdown, as well.

For instance, with thousands of their employees furloughed, national parks are likely to close. In the previous shutdown in January, about one-third of the country's national parks were closed — even following an agency directive to keep parks open.

U.S. housing authorities are also expected to see significant delays in loan processing and approvals.

Other institutions have announced preparations for a partial shutdown. The Smithsonian said it will be able to use existing funds to keep its 19 museums and national zoo open to the public through Jan. 1.

Smithsonian tweet

The Securities and Exchange Commission said on its website Friday morning that it also "will remain open for a limited number of days, fully staffed and focused on the agency's mission" if the government shuts down.

A spokesman for the U.S. Trade Representative said it "would be an agency affected by a lapse in appropriations."

"Essential personnel will be on-duty to ensure USTR continues to conduct all necessary operations, including trade negotiations and enforcement," the spokesman added.

-- CNBC's Mary Catherine Wellons and Jacob Pramuk contributed to this report.