A deal on U.S. aid for Ukraine and policy changes at the border with Mexico was left uncertain Monday as Congress returned with Senate negotiators struggling to reach an agreement and House Republicans trying to interject their own hardline immigration demands.

Senate negotiators met Monday and had hoped this week to present the details of a bipartisan bill aimed at reducing the number of migrants who travel to the southern border to apply for asylum protections in the U.S. But by the end of the day, senators said significant disagreements remained and predicted negotiations would be prolonged beyond this week.

“There’s too many unanswered issues that are still there. There’s too many unresolved parts,” said Sen. James Lankford, the lead Republican negotiator.

The small group of senators has already been working for months on the legislation after Republicans insisted on pairing border policy changes with supplemental funding for Ukraine.

President Joe Biden’s administration has also been directly involved in the talks as the president tries to both secure support for a top foreign policy priority — funding Ukraine’s defense against Russia — and demonstrate action on a potential political weakness — his handling of the historic number of migrants seeking asylum at the U.S. border with Mexico.

Biden has faced staunch resistance from conservatives to his $110 billion request for a package of wartime aid for Ukraine and Israel as well as other national security priorities. In the Senate, Republicans have demanded that the funding be paired with significant border security changes.

“The stakes here are quite high,” said Senate Republican Leader Mitch McConnell in a Senate speech earlier Monday. “We have an opportunity to make the most comprehensive headway on border security in a generation.”

But in the House, conservatives have criticized any proposals that fall short of the strict border measures they passed on a party-line vote last year. And some House members aligned with Donald Trump, the former president and current Republican presidential front-runner, have suggested they would not support any bipartisan proposal — no matter the substance — if it means giving Biden a border bill to sign in an election year.

House Speaker Mike Johnson, joined by about 60 fellow House Republicans, visited a Texas border city last week to press the case that the border legislation should tack closely to what the House has already passed. Johnson said the visit only increased his resolve to ensure border policy changes are included with Ukraine funding and called the House bill a “necessary ingredient.”

Over the weekend, congressional leaders reached a separate agreement on overall spending figures for the current fiscal year as they try to pass legislation to avoid a partial government shutdown in less than two weeks. But leaders made no mention of border policies or Ukraine aid, and some conservatives in the House have pushed to use the prospect of a government shutdown as further leverage in the negotiations over border policy.

White House press secretary Karine Jean-Pierre told reporters on board Air Force One on Monday that Republican should “stop threatening to shut down the government and fulfill their basic responsibility to fund critical domestic and national security priorities., including the president’s supplemental requests. It’s time for them to act.”

The White House has continually pressed Congress to approve supplemental aid for Ukraine, warning that the U.S. cannot send any more significant amounts of military equipment without approval. A lack of U.S. support would significantly diminish Ukraine’s defenses and weaken its government.

“It’s frustrating, but we’ll continue trying to get this nailed down,” said Sen. Chris Murphy, a Connecticut Democrat who has led negotiations for his party.

He added: “We’ve run out of time. Ukraine is at a real moment of peril. This is definitely an increasingly dangerous moment.”

Johnson has pointed to a deadline of providing the funding to Ukraine by February, saying that Ukrainian President Volodymyr Zelenskyy told him that was when funds would be needed during Zelenskyy’s December trip to Washington.

In the Senate, where negotiators have been plugging away at a bipartisan compromise, even Lankford, the head GOP negotiator, has acknowledged that the final agreement will not include all of the conservative priorities.

“We’re always focused on what it would take to pass a bill through the House, the Senate and receive the president’s signature,” Sen. Kyrsten Sinema, an Arizona independent central to the negotiations, said Monday.

As talks have progressed, the White House has tried to protect humanitarian parole, which it has used 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. But that has become a major sticking point in the negotiations, Republican senators said.

“We can’t fix asylum and then just have them release people on parole,” said Sen. John Cornyn, a Texas Republican. “That would be a disaster politically, and otherwise.”

Negotiators have also been grappling with how to implement a new series of border enforcement measures — many similar to those that were pursued by the Trump administration — that would be triggered if the number of daily crossings reach a certain threshold. It has proven difficult to reach agreement on what that threshold should be, according to people familiar with the talks who discussed the private negotiations on the condition of anonymity.

The emerging package also faces criticism from the left, with some progressive and Hispanic lawmakers raising concerns about policy changes that would restrict a migrant’s rights to seek asylum, which offers people protection from persecution in their home countries. Immigrant advocates critical of the proposal were planning to rally in Washington this week.

But the Biden administration has pressed forward in the negotiations as it looks to reduce the number of migrants arriving at the border.

Homeland Security Secretary Alejandro Mayorkas, who has been involved in the Senate talks, said during a Monday news conference in the border city of Eagle Pass, Texas that he was hopeful that Congress would provide “fixes to our broken immigration system” as well as billions of dollars that the White House has requested to bolster border security.

“Our system has not been updated for decades and yet the landscape of migration is so dynamic and so much different than it was years ago,” Mayorkas said.

(AP)