Congress is facing yet another familiar deadline this week: If lawmakers don’t pass a package of seven spending bills by midnight this Friday, the government could go into its second partial shutdown of the year.

Both Democrats and Republicans seem determined to avoid one, but as Trump’s acting Chief of Staff Mick Mulvaney told Meet the Press this weekend, “You absolutely cannot” rule out another shutdown, because Trump still wants his border wall and Democrats still do not want to give it to him.

Still, appetite for another shutdown seems low on the Hill, even as talks among a special House and Senate committee tasked with figuring out a border security agreement stalled this weekend — the sticking point seemingly over how much to allocate for Immigration and Customs Enforcement’s detention beds.

“I think the talks are stalled right now,” said Senate Appropriations Chair Richard Shelby during an appearance on Fox News Sunday. “I’m hoping we can get off the dime later today or in the morning because time is ticking away, but we’ve got some problems with the Democrats dealing with ICE, that is detaining criminals that come into the US, and they want a cap on them. We don’t want a cap on that.”

As things stand, Democrats want to cap the number of detention beds used for interior enforcement to curb ICE’s capacity to detain undocumented immigrants, while Republicans think this would hurt enforcement of deportation policies.

Disagreement over the detention beds as well as physical barriers is now threatening to throw congressional border security talks off kilter, with the deadline just days away. In the hope of preventing a shutdown, lawmakers are also looking at another short-term spending bill to tide them over until they are able to wrangle a larger compromise.

This is something a special committee of House and Senate lawmakers put in place after the shutdown concluded in January is tasked with resolving. If the committee fails to reach a deal by the Friday deadline or if the president is unwilling to approve the agreement reached by the committee, a portion of the government could again shut down.

As recently as last Friday, the Trump administration was suggesting that a shutdown could very well be imminent. “We’re on the verge of a government shutdown again,” Trump spokesperson Hogan Gidley said. “Because Democrats won’t come to the table and have a conversation about securing the country.”

In the meantime, Trump is scheduled to hold a rally in El Paso, Texas, on Monday evening to keep the pressure up on border security.

Detention beds are the latest sticking point in the spending bill

Although congressional lawmakers had been relatively optimistic about reaching a deal (Shelby said repeatedly that they’d have no problem reaching an agreement if left to their own devices), Democrats’ proposed cap on detention beds is proving to be a major point of contention.

As Bloomberg points out, Democrats are interested in limiting the number of detention beds used for interior enforcement so that ICE can focus its efforts on targeting criminals, rather than conducting broader raids on potential undocumented immigrants. Republicans, meanwhile, argue that capping the number of beds would hurt ICE’s ability to do its job:

There are currently 40,520 ICE immigration detention beds funded by Congress. Heading into the talks, the White House sought to increase the number to 52,000, while Democrats wanted a reduction to 35,520. Democrats have proposed a 16,500 cap on beds to be used for interior enforcement, with the rest to be used for those captured at the border, according to people familiar with the talks.

In addition to the back and forth over detention beds, the funding for border barriers — which was allocated at $1.6 billion in a previous Senate bill — also remains a major subject of debate.

This recent negotiations roadblock could stymie the hopes of lawmakers from both sides of the aisle, many of whom have been keen to avoid another shutdown.

While Democrats have long slammed the president’s use of a shutdown as political leverage for his border wall, Republicans aren’t particularly interested in the prospect of a second one either as the country continues to recover from the longest shutdown in US history.

Senate Majority Leader Mitch McConnell has especially hammered this point, noting in a recent press conference: “There certainly would be no education in the third kick of a mule.” And Republican after Republican has criticized the effects of the shutdown and the pain it caused hundreds of thousands of federal workers.

“I think there’s next to no appetite in the room on either side in either body, and that’s a good thing,” Rep. Chuck Fleischmann (R-TN), a member of the border security conference committee, told Bloomberg.

Congress had seemed on track to deliver some kind of deal on the matter, but the snags in the latest negotiations could very well thwart such goals.

Trump is also an ongoing wild card

The final unknown in all of this is still Trump. Even if lawmakers work out a deal including a boost in border barrier funding, it’s still unclear whether the president will back it.

If Trump doesn’t see the final agreement in keeping with the promise he made to his base during his 2016 campaign, it’s possible he could threaten another veto of any spending package that lawmakers cobble together. It’s also possible he would consider declaring a national emergency in order to secure the funds he wants for the wall, though this move has faced pushback from many members of his own party, who worry it could set a precedent for Democrats to do the same in the future.

If he considers either of these two routes, the pressure will be on Senate Republicans to push back. And while they’ve talked a big game about disliking both of these options, it isn’t clear just how far they would actually be willing to go to confront Trump.

With just a few days left to go, all the uncertainty both in Congress and the White House suggests that a shutdown could potentially still be on the table.