WASHINGTON, D.C. — A Senate deal to unlock billions of dollars in military aid for Ukraine looks increasingly unlikely to happen before the New Year, even as negotiators continue to try to reach an agreement.

Senate Democrats and the president are urgently trying to pass a $110 billion emergency supplemental funding bill before leaving town for the holidays. The bill includes funds for Israel, Ukraine, Taiwan and the southern U.S. border.

Republicans have said their sticking point in negotiations is immigration policy changes, amid a record surge in migrants arriving at the southern U.S. border.

Senate Minority Leader Chuck Schumer, D-N.Y., delayed holiday recess by a week to continue negotiations and was expected to schedule a vote by the end of the week.

Senate Minority Leader Mitch McConnell, R-N.C., said on Tuesday that while negotiations were making slow but steady progress, the details necessary for a vote would not be in place by the end of the week.

“Reaching an agreement that can pass Congress and become law is easier said than done,” McConnell said.

Democratic senators expressed frustration with the speed of negotiations.

“We should have done Ukraine three months ago. I’m still hopeful. I’m here to try to fix it and get things back on track,” said Sen. Sherrod Brown, D-Ohio, adding that senators had a duty to stay in town for a potential vote on the supplemental funding bill. “It’s my job. I’ll be here when I need to be here.”

A majority of Senate Republicans, however, have already left for their holiday break, saying there wasn’t enough time before the new year to hash out all their differences on border policy. Only 17 were present at a roll call vote Tuesday afternoon.

Top Biden administration officials said Ukraine can’t afford to wait any longer for more aid.

“We have one more security assistance package available to us before the end of this year, before we run out of replenishment authority, to replenish the stocks and the inventories on DoD’s shelves. That’s why it’s so critical that Congress act on that supplemental funding,” White House National Security Council spokesperson John Kirby said a briefing Tuesday.

Even if a deal is reached, the House has already adjourned for the holidays. Though highly unlikely, it could be recalled for a vote on the measure.

Punting the funding bill to January could result in further delays, as lawmakers will be occupied with 2024 appropriations bills. When Congress returns to session, there will only be 10 days to pass all appropriations bills before a potential government shutdown.