As Democrats and Republicans fight in the mud about immigration, border security, DACA, and children’s healthcare, there is one thing at stake bigger than all of them: the operation of the federal government. And if Congress cannot strike a deal by midnight on Friday, January 19, the federal government will shutdown, an economic effect on millions of dollars. If the Congress can’t reach a deal, it would be the first time in history that the government shutdown when both the White House and Congress were controlled by the same party.

But when the government shuts down, what does that really means? It means that federal employees and offices considered “non-essential” are closed and employees do not work, and subsequently do not get paid for the duration of the shutdown. Non-essential employees and offices include much of the federal bureaucracy including low-level office employees such as those at the Department of Commerce, Department of Agriculture, and Department of Interior, including all national parks and museums.

However, all federal employees and services considered essential still work and will receive back pay once the government is funded again. Essential services include, the Postal Service, Congress, all national security functions, including the Department of Homeland Security, the U.S. military and its 1.3 million active-duty service members, border security functions, and air traffic controllers, as well as federal prisons and law enforcement agencies, which will all remain open during the shutdown, despite uncertainty about future funding.

In addition, the government shutting down would mean a very uncertain future for more than 700,000 undocumented immigrants protected under DACA, as there is currently no long-term solution ahead of its March 5 deadline. The Children’s Health Insurance Program, which provides health insurance for roughly 9 million children, would only be funded through March. Whether Congress can come to an agreement still remains to be seen, but if they don’t, it will have negative effects on millions of Americans.