Here's what would happen if Trump's border wall demands force a government shutdown

According to a research memo prepared by congressional Democrats, roughly 800,000 federal employees would be affected by the shutdown.

About 420,000 workers would be deemed essential and would work without pay throughout the duration of a shutdown, while the other 380,000 workers would be put on furlough.

Read more: Here's what happens to Social Security and disability benefits during a government shutdown»

Certain departments would see larger numbers of furloughed employees, according to those agencies plans:

• 95% of NASA employees
• 95% of HUD employees
• 86% of Commerce Department employees
• 83% of Treasury Department employees

On the other end, only 14% of homeland security employees would be furloughed. Many of those employees deemed "essential" would be Border Patrol and ICE agents who are charged with protecting the US border. This would mean that those agents would work without pay until the shutdown ends.

While federal employees are not automatically repaid for missed wages, Congress typically passes legislation to give those workers back pay.

Lawmakers would still receive paychecks during a shutdown.

Since the budget process was overhauled in 1974, there have been 20 funding lapses.

While there are notable exceptions, most of these shutdowns have been short-lived. For instance, none of the eight shutdowns during Ronald Reagan's presidency in the 1980s lasted more than three days.

The longest shutdowns include a 21-day shutdown from December 1995 to January 1996 and an 18-day shutdown from September to October 2013.

One thing that is unique to the two lapses in 2018 is the one-party control of Congress and the White House.

The three day shutdown in January marked the first time that the government shut down under one-party control since the 1979 shutdown under President Jimmy Carter. It was also the first shutdown under one-party control that resulted in a furlough of federal employees.

If a shutdown occurs at midnight, this would also be the first time since 1979 when three funding lapses occurred in one calendar year.