The federal government shutdown continues on Tuesday, Oct. 21, officially marking three weeks with thousands of workers missing paychecks, flights increasingly delayed and lower-income families threatened with losing food assistance.

The current shutdown is the 15th since 1981 and is tied for the second-longest in U.S. history, lasting for 21 days. The prior standoff, which lasted from Dec. 1995 to Jan. 1996, was between the Republican-controlled Congress and then-President Bill Clinton, a Democrat, over how to balance the budget.

There are no votes scheduled on Capitol Hill on Tuesday, but Senate Republicans will be attending a luncheon at the White House, where Trump is expected to thank them for a united front during the shutdown fight and approving his nominees, according to Politico.

Here's a look at the latest of Day 21 of the shutdown

Is the federal government still shut down?

Yes, the federal government remains largely shut down and has been since just after midnight on Oct. 1.

More than 750,000 federal workers have been furloughed and ordered not to report to work. Employees deemed essential to public safety, including military personnel, law enforcement officers, border patrol and air traffic controllers, are required to work regardless.

While Trump signed an executive order directing the Pentagon to ensure active-duty military personnel are paid despite the shutdown, this doesn’t apply to all federal workers required to stay on the job.

What do Democrats and Republicans want for the government to reopen?

Democrats are pushing to ensure tax breaks for 24 million Americans who buy insurance through the Affordable Care Act (referred to as "Obamacare") and have refused to back a government spending bill that doesn’t address the issue.

The Senate Dems want to make the tax break permanent, which would otherwise expire at the end of the year, and provide reassurances to prevent the Trump administration from temporarily withholding funds.

Republicans and the president say they are open to considering a fix for the expiring ACA tax breaks, but want the issue addressed separately from the ongoing budget impasse. Republicans have also claimed that the Democratic proposal could partially pay for health coverage for people who are in the country illegally. That’s not true, according to the nonpartisan Congressional Budget Office.

What happens to Social Security, Medicare and Medicaid?

The Social Security Administration will continue to issue retirement and disability benefits but will furlough 12% of its staff and pause marketing campaigns, according to the agency’s shutdown plan.

Payments will likewise continue under the Medicare and Medicaid health programs.

Does the US mail get delivered?

The U.S. Postal Service is open because it does not depend on Congress for funding, USPS said in a statement.

What about the airports?

Over 13,000 air traffic controllers and about 50,000 Transportation Security Administration officers are required to show up for work during the shutdown, and neither group is expected to be paid until Congress approves a budget deal.

Will food aid continue under SNAP and WIC?

The Supplemental Nutrition Assistance Program (SNAP), the nation’s largest food aid program, and the Special Supplemental Nutrition Program for Women, Infants and Children, known as WIC, will continue operations as funds allow, according to the U.S. Department of Agriculture.

But the federal agency warned that there will not be enough funding to pay the entirety of SNAP benefits for November if the shutdown doesn’t end.

State health officials across the country, including in North Carolina, Wisconsin and Minnesota, have begun warning recipients of the possible lack of funds for November.

What does a shutdown mean for the military?

Trump signed an executive order directing the Pentagon to ensure active-duty military personnel are paid despite the federal government shutdown.

While 1.3 million active-duty military did get paid on Oct. 15, roughly 55% of the Defense Department’s 740,000 civilian employees have been furloughed, including those involved in training, procurement and administrative support. Civilians working in cybersecurity, medical care, weapons systems maintenance, intelligence and logistics are still working and are not included in Trump’s order to pay active-duty personnel.

National Guard forces that Trump has deployed to U.S. cities must also continue to work.

What about Homeland Security, immigration and border officers?

Only 5% of the Department of Homeland Security’s 271,000 workers have been furloughed, including those involved in research, planning, training and auditing.

The Department of Homeland Security confirmed on Oct. 16 that more than 70,000 sworn law enforcement officers across the department, including those serving in Customs and Border Patrol, Immigration and Customs Enforcement, Secret Service, Transportation Security Administration and other critical mission areas, will be paid for all hours worked during the shutdown.

Contributors: USA TODAY’s Zac Anderson, Fernando Cervantes, Amaris Encinas, Joey Garrison, Bart Jansen; and Reuters

This article originally appeared on USA TODAY: Is the federal government still shut down? Here's what we know on Tuesday, Oct. 21.

Reporting by Terry Moseley, USA TODAY / USA TODAY

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