Many Americans are probably wondering how a potential government shutdown would affect national security if Congress and the White House fail to reach an agreement on federal spending by the end of the month.

Military personnel would remain at work in the event of a shutdown, although they would not be paid until lawmakers make funds available for them. Only civilian defense employees would be subject to furloughs.

(U.S. Department of Homeland Security) (U.S. Department of Homeland Security)

That takes care of the Defense Department. But what about the agencies that fall under the Department of Homeland Security, such as Customs and Border Protection, the Coast Guard, the Transportation Security Administration — which handles airport screenings — or the Secret Service?

If past is precedent, the answers may lie in the contingency plans that federal agencies submitted in 2011, when the government last reached the brink of a shutdown — Congress ultimately reached a deal to avert that fate.

The DHS plan designated about 84 percent of the department’s roughly 230,000 employees that year as “essential,” meaning they would have remained on the job for the “safety of human life or protection of property.”

TSA would have retained about 87 percent of its workforce under a 2011 shutdown, while about 84 percent of Coast Guard and CBP employees would have remained on the job. Topping the list would have been U.S. Citizenship and Immigration Services, at 98 percent, followed by the Secret Service, with 89 percent.

For what it’s worth, USCIS is a fee-funded agency, and nearly 95-percent of its annual budget is comprised of the fees individuals pay to request immigration services and benefits, according to agency spokesman Christopher Bentley.

The most short-staffed DHS agencies would have been those that are lesser-known to the public. For example, the Science and Technology Directorate, which serves as the department’s research and development arm, would have kept only 3 percent of its 490-member workforce on duty, while just 6 percent of the Domestic Nuclear Detection Office’s 100 employees would have been exempt from furloughs.

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