US Sen. John Thune, a Republican from South Dakota, at the US Capitol on March 28 in Washington, DC.

Republican senators – including many who have long advocated for additional aid to Ukraine – warned Monday night they are prepared to vote against advancing a more than $100 billion supplemental national security package unless it includes major border policy changes, casting doubt on whether the aid will pass this year after border talks hit an impasse over the weekend.

Senate Republican Whip John Thune described the border talks as “in a bit of lull.” When asked whether the Senate might leave for the holidays without passing a bill, he put the onus on Democrats.

“I don’t know. It’s really up the Democrats. They are in charge up here,” he said. “I don’t think we do unless we have a border piece in it.”

Senate Democrats have said that border talks have stalled, while Sen. James Lankford of Oklahoma, the leading Republican negotiator, indicated Monday night that things could still get back on track and Minority Leader Mitch McConnell insisted during his floor speech that Republicans remain at the negotiating table.

But with time running short and senators scheduled to be in Washington for just two more weeks, one option would be for Majority Leader Chuck Schumer to move to advance an aid package without the border policy changes and dare Republicans to vote no on additional aid to Ukraine and Israel, which has been an important priority for many Senate Republicans. Schumer would need nine Republicans to overcome a procedural hurdle, something that many Republicans signaled Monday they wouldn’t help Democrats do.

“It may require a failed cloture vote on the supplemental before Sen. Schumer realizes we are serious,” Sen. John Cornyn, a Texas Republican, told reporters.

Other members agreed.

“I am opposed to moving forward on cloture,” West Virginia GOP Sen. Shelley Moore Capito, a member of the Senate Appropriations Committee, said Monday. “I’m not opposed to a national security supplemental at all, but it has to include our own national security at the border.”

Lankford similarly predicted that such a vote would fail.

“I don’t want to have a failed vote on anything,” Lankford said. “If Schumer brings it up, it will certainly fail. On that point, I don’t think that it proves anything other than everyone knows where we are on this.”

Iowa Sen. Joni Ernst, who has been a strong supporter of Ukraine aid, said she wanted to see additional funding for Ukraine, but “we have to have border” policy changes. She added she too would vote against advancing the supplemental package if “we don’t have substantial changes” to border policy.

Sen. Chuck Grassley, also of Iowa, echoed Ernst’s remarks.

“I don’t know how you get 60 votes to bring that up without that in it,” Grassley said.

The Senate is just part of the hurdle Schumer faces at the end of the calendar year. Even if lawmakers could get a supplemental package out of the Senate, House Speaker Mike Johnson is balancing his own politics in the GOP-controlled House, where hardliners are demanding not just border policy changes but changes that closely mirror the House-passed border bill from earlier this year. Johnson has made his conference dynamics clear to GOP leaders.

Republicans have argued that the White House and President Joe Biden specifically should be motivated to cut an aggressive deal on border security given the growing influx of immigrants at the southern border and the challenge it poses to the president in his reelection. But Thune complained Monday the White House “hasn’t gotten the sufficient level of seriousness yet” about the border crisis.

But Democrats are accusing Republicans of demanding far too much in the talks.

“Until Republicans are willing to drop their most extreme demands and sit down and have an honest conversation, we’re stuck,” said Democratic Sen. Chris Murphy of Connecticut.

Murphy warned US allies should “be very worried about what Republicans are doing.”

“Listen, I have all sorts of domestic priorities I care about. I could demand that Republicans pass changes in our background checks laws as a condition of my vote for Ukraine, but I don’t do that because Ukraine is too important because this is the future of the world,” Murphy said.

Murphy added the chances are increasing every day that Congress leaves without passing more money for Ukraine, but he said, “Sometimes there are moments when you can’t fail.”

It’s perhaps one of the most precarious moments yet for aid to Ukraine and Israel that – in theory – have broad, biparti