WASHINGTON (AP) — Amid grueling negotiations, the contours of a bipartisan border security and immigration deal are beginning to take shape, emerging even as Congress leaves town having failed to publicly unveil any details of the package that’s central to unlocking stalled aid for Ukraine.

Talks between the White House and key senators have not veered widely from three main areas of discussion: toughening asylum protocols for migrants arriving at the U.S.-Mexico border; bolstering border enforcement with more personnel and high-tech systems; and deterring migrants from making the journey in the first place.

As the Senate broke for the holidays, due back Jan. 8, Senate Majority Leader Chuck Schumer and Senate Republican Leader Mitch McConnell in a rare joint statement indicated negotiations are progressing. They also met Wednesday to discuss how to advance the border policy alongside President Joe Biden’s$110 billion package of wartime aid for Ukraine, Israel and other national security priorities.

“We all know there’s a problem at the border,” Schumer said before sending senators home. “Our goal is, as soon as we get back, to get something done.”

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McConnell said the negotiations “continue to make headway.”

And as aid for his country hangs in balance, Ukrainian President Volodymyr Zelenskyy said at his own press conference in Kyiv he was confident “the U.S. will not let us down.”

Here’s a look at what’s being discussed as key Senate negotiators and the White House plan to dig in during the weeks ahead:

TOUGHER ASYLUM CLAIMS

Senate negotiators have focused on asylum, by which the U.S. offers protection for people facing persecution in their home countries. The senators say they are trying to ensure that migrants who have a credible claim to asylum can safely apply, but that officials can also quickly turn away those who don’t qualify.

Critics often say that too many people who pass their initial asylum interview end up ultimately failing in their efforts to win asylum. But because the immigration courts are so backlogged by the time the final determination happens, many have been in the country for years, making it more difficult and expensive to deport them.

The senators and the Biden administration have considered toughening the so-called credible fear standard that’s used in the initial interviews to determine if migrants seeking asylum would likely have a winnable case before an immigration judge.

Advocates for immigrants argue that the credible fear standard is deliberately low in recognition of the fact that migrants being interviewed have usually fled desperate conditions, don’t have legal representation and are still shaken by their journeys.

BORDER SECURITY

It was the Republicans who demanded negotiations over the border, refusing to provide aid for Ukraine as it battles Russia’s invasion, unless Biden also agreed to changes to cut immigration.

While Biden had initially proposed $14 billion to bolster border security in the national security package, Republicans said money was not enough. They want to enshrine policy changes at the border into law, some echoing Donald Trump, the party’s frontrunner for the presidential nomination, who takes a hard line against immigration.

Still, billions of dollars of funding will almost certainly be part of any deal.

Border Patrol officers are overwhelmed processing migrants who turn themselves in seeking asylum. Biden had proposed $3.1 billion for additional border agents as well more asylum officers, immigration judge teams and processing personnel. Supporters say the money for the asylum system is crucial to addressing the backlog in immigration courts and essentially getting the process moving faster.

Biden has also suggested $1.2 billion for Customs and Border Protection officers and inspection systems to stop the flow of deadly fentanyl.

While the president also proposed funds to help communities in the U.S. that are taking in the record numbers of new arrivals, Republicans have resisted sending money to the cities, largely Democratic, that are helping house and provide care for the migrants.

REDUCING BORDER BUILD-UP

Over and over, senators have emerged from hours of closed-door talks with an exasperated conclusion: Immigration policy is complicated.

“Millions of decisions,” said Sen. James Lankford, a Republican of Oklahoma. “Underneath every big idea is 100 smaller decisions that all have to be made, and every one is complicated.”

Sen. Chris Murphy, Democrat of Connecticut, said: “It’s interconnected. So if you press in one side and it pops out the other, it takes time to get this right.”

One of the toughest issues to resolve has been how to dissuade migrants from even embarking on their journeys to the U.S. in the first place, particularly from countries experiencing unrest, economic calamity or widespread gang violence.

Senators have discussed ways to encourage people to apply for asylum before they arrive at the border — either in their home country, or if that’s not plausible, a country they travel through on their way to the U.S.

The Biden administration had launched a new system earlier this year that encourages people seeking asylum to schedule an appointment, via a smartphone app, to seek entry at the border.

In talks, the White House has also insisted on keeping in place its ability to allow 30,000 people a month from Venezuela, Nicaragua, Cuba and Haiti entry into the U.S. if they have a financial sponsor and fly into the country.

The idea is to create a more orderly, efficient asylum system that reduces chaos at the border.

But record numbers of migrants are still arriving. Illegal crossings topped 10,000 some days in December.

ENFORCEMENT

Negotiators have run into trouble in the talks when it comes to enforcement measures. One potential compromise would set a threshold for the number of border crossings, and once the number is reached, stricter enforcement measures would take effect.

Under that system, if the crossings get too high authorities would shut down the border for asylum claims, enable fast-track removals of migrants who have already entered unlawfully, and detain some migrants while they are screened for valid asylum claims.

Funding in the package could also go to bolstering immigration enforcement, including detention facilities, according to one person familiar with the private negotiations who spoke on the condition of anonymity.

Advocates for immigrants worry that some of the restrictions under discussion could just push the build-up of migrants south of the U.S.-Mexico border.

“We’re turning Mexico into a staging area for migrants moving north,” said Dylan Corbett, who heads the Hope Border Institute, in a call with reporters. “Mexico doesn’t have the infrastructure to be able to deal with this.”

They also warn that the expedited removal measures would strike fear in the millions of immigrants lacking permanent legal status while effectively turning Trump-style administrative policies into law, making them potentially more difficult to challenge in court.

Sen. Kyrsten Sinema, an Arizona independent central to the negotiations, said that the potentially lasting impact of their work hangs over the talks.

“A mistake here will matter for many years,” she said.

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Associated Press writer Elliot Spagat contributed to this report.