When Congress comes back to town this week, lawmakers will have just days to confront the gridlock that is threatening to leave the Department of Homeland Security (DHS) without funding for its operations after February 27.

When Congress approved a $1.1 trillion spending bill in December, they purposefully let DHS funding expire in February to appease conservatives who wanted a chance to challenge the president's immigration policies in the newly Republican Congress. Now, they must confront the issue once again. Republicans want a bill that blocks Mr. Obama's executive actions that would shield millions of immigrants in the U.S. illegally from deportation, while Democrats argue the president is acting within his authority and are pushing for a so-called "clean" bill.

The House passed a bill in January that undoes the president's executive actions, but it can't make it past Democratic objections in the Senate. Some lawmakers, including Sens. John McCain, R-Arizona, Lindsey Graham, R-South Carolina and Bob Corker, R-Tennessee, are hoping that a recent court decision challenging the president's immigration policies will be enough to convince lawmakers not to let funding expire.

On CBS' "Face the Nation," McCain called it an "exit sign" to the controversy. Corker said on NBC's "Meet the Press" he was "gratified" by the judge's ruling and that the department needs to be fully funded. On ABC's "This Week," Graham said, "I am willing and ready to pass a DHS funding bill and let this play out in court. The worst possible outcome for this nation is to defund the Department of Homeland Security given the multiple threats we face to our homeland. And I will not be part of that."

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He said he hoped his colleagues in the Republican-led House would understand that "our best bet is to challenge this in court" and avoid the risk that they would be blamed by the country.

What the House will do is the big X factor, as Speaker John Boehner, R-Ohio, said last week on Fox News Sunday that he's "certainly" prepared to let funding expire if the Senate doesn't pass the House version of the bill.

Here is what would happen if DHS runs out of money on Friday:

1. Most DHS employees go to work but can't collect a paycheck: DHS employs about 230,000 people, but the vast majority of them are considered essential employees that must report to work even if the agency is unfunded. Just 30,000 people would be furloughed if Congress didn't approve the money to keep it running.

"People on the front lines, aviation security, maritime security will be forced to come to work without a paycheck. And so for the working men and women of my department to have to work without a paycheck is very significant and very serious. And Congress needs to appreciate that," DHS Secretary Jeh Johnson said on CNN's "State of the Union" Sunday.

In another interview on CBS' "Face the Nation," he suggested that the majority of those employees are at the agency's headquarters in Washington - and that would make it harder for the U.S. to stay ahead of challenges that DHS faces.

"I'm pushing my headquarters staff to stay one step ahead of [the Islamic State of Iraq and Syria], one step ahead of our challenges on aviation security, one step ahead of monitoring our illegal migration, our border security on our southern border. If we shut down, my headquarters staff is dialed back to a skeleton and so that hampers our ability to do that," he said.

2. Immigration functions largely continue, except for E-Verify: Much of U.S. Citizenship and Immigration Services (USCIS) is funded by the fees that people pay for visa applications and renewals, meaning that the agency isn't reliant on money appropriated by Congress. But, as Vox reports, the E-Verify program - which allows employers to check the immigration status of their employees - is dependent on Congressional funding. Republicans tend to be more supportive of the program than Democrats, and would have to grapple with this reality.

Most employees at USCIS and Customs and Border Protection (CBP) still report to work. According to a document DHS prepared of the 2013 government shutdown, 12,205 of 12,558 USCIS employees would have reported to work in the absence of funding, and 52,673 of CBP's 59,561 employees would have as well.

3. States and local governments lose out: While most of the essential functions within DHS will continue, the agency won't dole out money to its state and local partners through the grant process. "Our grant-making activities to state and local law enforcement, to commissioners, sheriffs, chiefs grinds to a halt," Johnson said on CNN.

4. FEMA employees will mostly report for duty: Johnson said in the same CNN interview that "something like 80 percent" of the Federal Emergency Management Agency's (FEMA) "permanent appropriated workers" would stay home. That statement ignores the fact that many of the agency's workers aren't funded through the annual appropriations process, according to a Factcheck.org review. The 2013 DHS report found that that 78 percent of FEMA's 14,729 employees would stay on the job if the agency went unfunded. Plus, more than one-third of FEMA's disaster workforce comes from reservists, according to a Government Accountability Office report, and they aren't reliant on annual funding from Congress.

5. The Secret Service can't begin hiring for agents to protect the 2016 presidential nominees: The Secret Service is already having a terrible year, plagued by multiple security breaches and scandals that led to the resignation of former director Julia Pierson and other top executives. A DHS funding lapse won't do them any favors. Most Secret Service agents stay on the job during a shutdown scenario -- 6,003 out of 6,537 people who work for the Secret Service, according to the 2013 DHS report. But Johnson said during a speech in late January that the agency would not be able to hire agents for the next presidential election (or make other improvements called for in a recent review) if agency funding goes dry.

"This means we cannot invest in the things the independent panel recommended to improve the Secret Service; we cannot hire new Secret Service agents for the coming presidential election cycle," Johnson said during the speech at the Woodrow Wilson Center.

A previous version of this article stated that Congress reconvenes Tuesday. The Senate goes into session Monday.