Why are some Republicans opposing more aid for Ukraine?

US aid to Ukraine is at a standstill, ground to a halt by mounting opposition from Republicans despite dire warnings from the White House and Kyiv.

While many are supportive of helping Ukraine, some have insisted that continued aid be tied to sweeping US immigration and asylum reforms.

Other conservative lawmakers have taken a harder line, opposing further Ukraine aid on ideological grounds.

Without their support, US assistance to Ukraine could run out by year's end.

Republicans' reluctance to help Ukraine without significant concessions was starkly highlighted earlier this week. With just days to go until Congress heads home for its scheduled winter break, Senate Republicans blocked a procedural vote to advance a national security bill that includes $61bn (£48.5bn) for Ukraine.

Democrats appeared pessimistic in the aftermath of the vote.

"I just don't know how this is going to sort itself out. The Republicans are taking a really incredibly hard stance on this," a Senate Democratic official told BBC News. "They're saying this is not a negotiation - this is a demand."

Let's take a look at why Republicans voted down Ukraine aid.

Seeking national security concessions

National Security Council spokesperson John Kirby said at a White House press briefing on Thursday that the White House is contending with "a small number of Republicans who want to hold that aid hostage for some pretty extreme border policies".

But much of the recent public opposition to the funding bill came from lawmakers - such as Senate Republican leader Mitch McConnell and South Carolina's Lindsey Graham - who remain supportive of Ukraine aid.

Mitch McConnell and other Republican lawmakers voted down Ukraine aid after failing to tie it to concessions on border security.

Rather than oppose helping Ukraine on ideological or political grounds, these Republicans have sought to use the issue as a way to accomplish other policy goals. Their key aims include tougher border security, immigration and asylum measures at the US-Mexico border.

"I have no less enthusiasm for the package," Mr McConnell told the New York Times, referring to the aid package. "I think it's critically important. We'll get there."

He added, however, that he does not believe it is "unreasonable" to club the issue together with the immigration debate.

Justin Buchler, a political science professor at Case Western Reserve University in Ohio, told the BBC that this wing of the party has "adopted a strategy of legislative hostage taking" to accomplish its aims, a tactic that began during the administration of Barack Obama.

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"Large segments of the party have decided, essentially, that when there are branches of government held by Democrats, they will look for any hostage they can take," he said. "That's what is happening now."

Republicans that fall into this category have repeatedly said that they are open to negotiating with their Democratic counterparts and working with President Joe Biden until an acceptable compromise is made. President Biden has said he is willing to do "significantly more", potentially paving the way for the Senate to advance the funding bill.

Senator Graham - who recently referred to Russia's invasion of Ukraine as "barbaric" - said he was "encouraged" by the comments.

"It's going to take his leadership or we are stuck," he told reporters.

Ukraine has said it sees foreign assistance as vital to its war effort.

Ideological opponents

Other Republicans have taken a markedly more hard-line approach to Ukraine funding, with some arguing that, on principle, that the assistance is misguided or wrong.

This position has been taken by a small but vocal minority of lawmakers from the hard right of the party, such as Representatives Matt Gaetz, Jim Jordan, Marjorie Taylor Greene, who has said Ukraine aid "puts America last" and means that "we're ignoring our own people's problems".

These members of a growing isolationist wing of the Republican party appear motivated by Donald Trump. The former president has repeatedly questioned aid to Ukraine and refused to commit to supporting Kyiv.

Instead, he has said that he would end the war "in 24 hours". He also called on Congress in July to withhold aid to Ukraine until the Justice Department and FBI "had over every scrap of evidence" about any alleged Biden family misdeeds.

"Quite frankly, Donald Trump is opposed to anything that President Biden is in favour of and that would be beneficial to the Biden presidency," Glenn Altschuler, a professor of American Studies at Cornell University, said.

While this wing of the party remains relatively small and unable to block legislation on its own, Mr Altschuler said it can "have an outsized influence, at least on the moment, on the outcome".

Slipping support among voters

Polls have shown that support for Ukraine is slipping among the broader electorate, particularly Republicans. A November Gallup poll shows that 62% of Republican voters now believe the US is doing too much to help Ukraine. In June, the figure stood at 50%.

Other polls have shown that Republicans are significantly more likely to view the US-Mexico border as one of the most important issues facing the US, and that voters of both parties are concerned. A recent Quinnipiac University poll found that 64% of voters disapprove of Mr Biden's handling of the border - including 95% of Republicans.

While most Republican lawmakers have not cited changing voter sentiment as a reason for opposition to Ukraine aid, the combination of the two issues can potentially give them a significant political boost.

"There's a significant political upside to tying Ukraine to border security and calling attention to the immigration crisis at the border, largely because they believe it is the most potent political weapon for the Republican Party," Mr Altschuler said.

"They can do this because support for Ukraine has waned somewhat, and therefore does not have a downside."