Today, the pain of a partial government shutdown will become all too real when an estimated 800,000 federal workers miss a paycheck.

“Once that first paycheck [doesn’t come], we’re no longer talking about the theoretical; we’re talking about tangible missing of paying electric bills, paying mortgage or rent — at which point, the narrative shifts,” says High Point University political science professor Brandon Lenoir.

The partial shutdown, which began on December 22 and affects nine federal departments, seemed fairly low-risk at first, since it didn’t involve the entire government and many affected agencies had funding through the end of the year. But as it stretches on, tying for one of the longest government shutdowns in history, the liability for federal workers — many of whom are facing post-holiday bills — is starting to set in.

As an official for the American Federation of Government Employees, a union for government employees, told NBC News, workers in the departments that have yet to be funded will begin to see the effect of the shutdown between January 11 and 17, when paychecks that cover the December 22 to January 5 pay period are typically sent out. Already, thousands are beginning to apply for unemployment or consider other part-time work.

“If we don’t have an agreement I think by midnight on the 8th, which is Tuesday, then payroll will not go out as originally planned on Friday night,” acting White House Chief of Staff Mick Mulvaney said during a Meet the Press appearance over the weekend. That deadline has come and gone and Democrats and Republicans are nowhere close to a possible spending deal.

Friday’s missed paycheck could very well force President Trump and other Republican lawmakers to consider the fallout for workers much more seriously, marking a key inflection point in the substance — and optics — of the shutdown fight.

The shutdown is about politics for politicians — but it’s real for federal workers

While Trump continues to levy aggressive demands for a border wall, one of his chief campaign promises, many federal workers are trying to figure out how they’ll cover immediate costs like rent, utilities, and medication — concerns the president has brushed aside.

As federal workers continue to share stories about the financial hardship they’re experiencing and the effect it has on their families, Trump has responded with little more than a shrug — repeatedly discounting workers’ struggles and going so far as to argue that the partial shutdown has a “higher purpose than next week’s pay.”

The risk of public outcry potentially escalating after that first missed paycheck hasn’t escaped Senate Republicans, including a handful who will be vulnerable during the 2020 election cycle.

“I think that’s gonna elevate the debate because thousands and thousands of employees are going to miss their paychecks,” Senate Appropriations Committee Chair Richard Shelby (R-AL) told Government Executive.

The Republican-dominated Senate has thus far taken no action to address federal worker concerns — refusing to consider spending bills proposed by House Democrats as part of efforts to reopen the government. As worker blowback about this approach grows come Friday, that position just might begin to waver.

“Every day this shutdown continues is another day of increasing anxiety for federal workers and everyone affected by these political games,” AFGE president J. David Cox Sr. said in a statement. “The pain will certainly hit home this Friday when the paychecks stop coming and 800,000 workers must figure out how to survive without any income.”

This collective missed pay amounts to a whopping $2 billion, according to an analysis by the Center for American Progress, a left-leaning think tank. It’s worth noting that in past shutdowns, Congress has typically approved back pay for employees after the shutdown ends — but it is a norm rather than a law, and there is no guarantee that Congress will do that again this time around.

Outcry is only expected to build — and put pressure on Republicans

Trump repeatedly claimed that federal workers — particularly Border Patrol agents, who are working without pay — support his efforts to shut down the government, but the vehement pushback he’s received from several of the largest unions representing government employees indicates that most don’t. What’s more, a December survey from the Government Business Council and GovExec.com found that seven in 10 government employees actively disagree with the partial government shutdown. (Representatives from the Border Patrol union have stood by Trump, however.)

To make their opposition all the more clear, several key unions representing federal workers plan to dial up their pushback toward the shutdown via a slew of protests this week, with AFL-CIO and AFGE among those spearheading a rally outside the White House on Thursday. Members of 32BJ-SEIU, a union representing building service contractors, are also targeting vulnerable Republican senators as part of calls they’re making to Congress, according to a spokesperson.

And while Democrats have been the ones most prominently highlighting the impact on federal workers during this shutdown, Republican lawmakers haven’t been immune to the outpouring from federal employees about the challenges they’re facing without their expected paychecks. “We don’t need to hold them hostage,” Sen. John Boozman (R-AR) told CNN, when discussing workers who may live paycheck to paycheck.

Many of the unions’ latest efforts are aimed at keeping the focus on the pain the shutdown is causing federal workers, with the goal of pressuring Senate Republicans — including those facing a tough reelection fight in 2020 — to change course.

“The only group to possibly crack, if the pressure is great enough, are Senate Republicans looking ahead to 2020 elections,” says Eileen Babbitt, a professor of conflict analysis and resolution at Tufts University’s Fletcher School of Law and Diplomacy. “If they feel the president is finally going too far off the rails, they could publicly break with him. That would truly be an inflection point, as it will signal a major split in the Republican coalition.”

Already, a growing number of Republicans including Sens. Cory Gardner (CO), Susan Collins (ME) and Lisa Murkowski (AK) have split with the president on this issue. As CNN reports, more and more Republicans are also expressing an openness to considering individual spending bills that would reopen noncontroversial agencies one by one, which House Democrats intend to pass this week.

It remains to be seen how many will ultimately go this route as worker pressure intensifies.

Something big needs to happen for the stalemate to break

Although Republican backing for Trump’s wall is clearly waning, it would still take a pretty dramatic turn in public opinion for a large-scale defection in the Senate conference. This is, in large part, because Trump’s base of support still remains relatively synonymous with the Republican voter base in a number of right-leaning states.

“It is possible that some Republicans, particularly senators with many affected federal workers in their states, might be inclined to push for a resolution without wall funding — but many of these senators are in Western states where their bases are also Trumpian,” says University of Maryland Baltimore County political science professor Roy Meyers.

States like Utah, South Dakota, and Montana have a high proportion of federal workers who are in their jurisdiction, for example, but they’re also states that went for Trump by double digits in 2016. Public opinion will likely have to sour significantly on the president and the wall standoff to compel certain Republican lawmakers to consider voicing some opposition, especially since the next election is still many months away.

That hasn’t appeared to happen ... yet.

“What’s missing so far is public urgency, where voters say, ‘Do something about this — or else!’’’ says George Mason University political science professor Bill Schneider. Recent polls show Trump’s approval ratings taking a major hit in the wake of the shutdown, but much of this criticism remains split along party lines.

With federal workers set to miss their first paychecks on Friday, that dynamic could certainly begin to change.