Funding for nine federal departments and multiple agencies expired at midnight Friday, which means that more than 420,000 employees will work without pay and another 380,000 will be furloughed, according to the New York Times.
Even a partial shutdown of select departments will prove problematic, experts say.
A timeline of the past federal shutdowns
Feb. 9, 2018 (one day)
Why? A budget agreement featuring an increase in military spending, disaster relief funds and an extension to CHIP was denounced by many, including House Minority Leader Nancy Pelosi and Sen. Rand Paul for not addressing immigration and protecting DACA's recipients (or "Dreamers").
Then what? Congress agreed to the $400 billion deal, which Trump signed.
Jan. 20-22 2018 (three days)
Why? A Senate immigration bill under Trump failed to pass. Democrats wanted the bill to address the funding of the Deferred Action for Childhood Arrivals (DACA) program, but Republicans said the deadline wasn't until mid-March.
Then what? Democrats reached a compromise to continue negotiations until Feb. 8. "If an agreement isn't reached by February 8, the Senate will immediately proceed to consideration of legislation dealing with DACA," Senate Minority Leader Chuck Schumer previously said.
» RELATED: The Latest: Digging in, Trump warns of 'very long shutdown'
Oct. 1-17, 2013 (16 days)
Why? Ted Cruz and House conservatives insisted on delaying Obamacare, which President Barack Obama rejected. The House passed multiple versions; the Senate kept sending them back.
Then what? Minor changes were made to Obamacare, including income verification requirements, before Obama signed the spending bill. Congress voted to extend the debt limit as well.
Dec. 5, 1995 to Jan. 6, 1996 (21 days)
Why? The longest shutdown in U.S. history deals with that provision to balance the budget within seven years. Republicans wanted Clinton to use the Congressional Budget Office's economic forecasts, not the more optimistic Office of Management and Budget forecasts.
Then what? Nothing, really. Republicans gave in and Clinton submitted a plan with CBO forecasts ensuring a balanced budget within seven years.
Nov. 13-19, 1995 (five days)
Why? Former President Bill Clinton vetoed Congress' resolution packed with provisions he opposed, including increased Medicare premiums.
Then what? As negotiations continued, Congress agreed to fund the government at 75 percent levels for about a month. And despite his initial opposition, Clinton agreed to a provision to balance the budget within seven years.
Oct. 5-9, 1990 (three days)
Why? Former President George H.W. Bush vetoed a spending bill without a deficit reduction plan, which he demanded. The House was unable to override the veto.
Then what? Congress came up with a joint resolution with a deficit reduction plan. Bush signed it.
Dec. 18-20, 1987 (one day)
Why? Democrats wanted more funding for Nicaragua's Contras and wanted to reinstate the "Fairness Doctrine" requiring balanced political coverage by broadcasters.
Then what? The Contras received nonlethal aid, but the Democrats gave up on reinstating the "Fairness Doctrine."
Oct. 16-18, 1986 (one day)
Why? Lots of disagreements between Democrats and Reagan's White House, including a Democrat measure to expand Aid to Families with Dependent Children (welfare). Time ran out before all parties could come to a resolution.
Then what? Democrats dropped some demands but secured welfare expansion and concession regarding privatization of the public railway, Conrail.
Oct. 3-5, 1984 (one day)
Why? The three-day extension (see below) came and went.
Then what? Congress let go of both the civil rights issue and water projects package and passed Reagan's desired crime-fighting measure. Unrelated to the previous shutdown disputes, temporary funding was also decided for Nicaragua's anti-communist Contra guerrillas.
Sept. 30 - Oct. 3, 1984 (two days)
Why? A spending bill that passed in the House included a crime package Reagan wanted, but it also included a water projects package he opposed. In addition, Democrats sought a reversal of the Title IX Civil Rights Act Grove City College v. Bell Supreme Court decision, which allowed exemptions for colleges that didn't get federal funding but whose students did. Reagan opposed this as well.
Then what? A deal wasn't reached in time, so the negotiations continued with a signed spending extension.
Nov. 10-14, 1983 (three days)
Why? Reagan's disputes over foreign aid spending cuts and increases, plus the Democrats' $1 billion education spending bill, led to a short shutdown.
Then what? House Democrats cut the spending down to roughly $100 million and funded the MX missile Reagan wanted, but maintained their proposed foreign aid and defense cuts. They also got a ban on wildlife refuge for oil and gas. The new bill also banned federal employee health insurance coverage to fund abortions unless the mother's life was in danger.
Dec. 17-21, 1982 (three days)
Why? Two main reasons. Reagan wouldn't sign two proposed spending bills to create jobs. And the House refused to fund Reagan's Cold War MX missile program against the Soviet Union.
Then what? None of the aforementioned issues were funded. The House proposed funding for legal support for poor Americans and increased funding for Israel, which Reagan signed into law after criticizing both strategies.
Sept. 30-Oct. 2, 1982 (one day)
Why? Congress didn't pass new spending in time because leaders were, well, busy. "President Reagan invited all members of Congress to a barbecue at the White House, while Democrats were having a $1,000-a-plate fund-raising dinner," the New York Times reported in 1982.
Then what? Nothing. Spending bills were signed a little later.
Nov. 20-23, 1981 (two days)
Why? Former President Ronald Reagan vetoed a package of domestic budget cut legislation $2 billion short of how much he sought.
Then what? A temporary bill extended spending through Dec. 15 to allow time for a long-term resolution.
Sept. 30 to Oct. 12, 1979 (11 days)
Why? The House wanted to limit federal abortion spending to the stricter restrictions (mother's life in danger) but the Senate wanted to keep funding abortions in cases of rape, incest and heightened mother's health risk. The House also wanted to raise congressional and senior civil servant pay by 5.5 percent, which the Senate opposed.
Then what? The compromise previously set on Medicaid and abortion was tightened to allow funding in cases of rape, incest, but not when the mother's health was in danger. Funding was allowed, however, if her life was in danger. The House also received its 5.5 percent pay increases.
Sept. 30 - Oct. 18, 1978 (18 days)
Why? Carter vetoed a defense bill Congress passed, which included funding for a nuclear-powered aircraft carrier. He also vetoed a public works bill. Both, he believed, were wasteful projects. The abortion dispute also added to the funding gap.
Then what? In the end, the previously vetoed bills were adjusted to exclude the projects Carter opposed and the previous compromise on abortion remained.
Nov. 30 - Dec. 9, 1977 (eight days)
Why? The second measure to allow more time for negotiations on the abortion issue failed. The Senate proposed Medicaid dollars be used for abortions by victims of statutory rape, which the House rejected.
Then what? They eventually brokered a deal to allow Medicaid to also pay for abortions resulting from rape or incest or abortions necessary to protect the mother and her health.
Oct. 31 - Nov. 9, 1977 (eight days)
Why? Unfortunately, the abortion dispute continued despite the temporary measure for resolution.
Then what? Carter signed another bill to give Congress more time.
Sept. 30 - Oct. 13, 1977 (12 days)
Why? The Senate under former President Jimmy Carter sought looser restrictions on Medicaid use to cover abortions, specifically for funding in cases of rape, incest or when the mother's health was at risk, before the Sept. 30 deadline. But the House wanted to maintain the restrictions of the time, which only allowed Medicaid dollars to cover abortions if the mother's life was at risk.
Then what? The funding gap ended Oct. 31, and negotiators were given more time to come to a resolution through a temporary measure ending the shutdown.
Sept. 30 - Oct. 11, 1976 (10 days)
Why? Former President Gerald Ford vetoed a funding bill for the Departments of Labor and Health, Education, and Welfare (or HEW, now split into the Departments of Education and of Health and Human Services).
Then what? Congress overrode the veto, but it wasn't until Oct. 11 that its continuing resolution to end the funding gap for other parts of the government went into effect.