To put it simply there are fairly influential people in the US who argue that Ukraine is not a 'vital interest' to the US. They may phrase this is various ways, and sometimes walk back from the sharper pronouncements, but the idea is basically the same.
This used to be articulated in more detail in the past, e.g. in 2014 one could read:
Once, foreign policy experts talked about “vital interests." The term has fallen into disuse, partly because there are no hard and fast rules for calculating what distinguishes the "vital" from the merely "interesting." If advocates wanted their country to do a thing they would call it a vital interest; if they did not, then they would not. But students of foreign policy did seem to agree on one thing: vital interests were the things you were willing to have your soldiers die for and kill for. By this measure, even the most hawkish politicians in the United States, all of whom have eschewed any desire for a shooting match, have agreed that the United States has no vital interests in Ukraine.
What would vital interests look like if they were present? Vital interests affect the safety, sovereignty, territorial integrity, and power position of the United States, or indeed of any country. If, in the worst case, all Ukraine were to "fall" to Russia, it would have little impact on the security of the United States. Russia is no longer the strong country that the USSR was: its GDP is dwarfed by that of the United States. Its non-nuclear military power is woefully insufficient for the conquest of the major states of Eurasia. The possession of Crimea, a grab for Ukraine's eastern provinces, or even the occupation of all Ukraine would not change this.
That piece also argues (mistakenly IMHO) that Belarus is a rather neutral 'buffer zone', not hosting Russian bases/forces, so that if Ukraine ends up like Belarus is no big deal, little would change in terms of NATO-Russia positioning of forces. So, yeah generally one version of the argument is discounting the strength and importance of Russia's presence anywhere.
And of course, there are those who say that the US shouldn't be in NATO much if at all, at least not with troops/bases. A version of this idea is that the US should be all-focused on countering China:
The United States cannot maintain its role as the cornerstone of European security while successfully competing with a growing China forever.
And that additionally US Asia's allies should also be paying more to maintain their independence from China:
And the cheap‐riding that afflicts the U.S. alliance in Europe also addles its alliances in Asia.
This version of the claim is that US is paying too much for all their allies security, essentially, while the latter are 'free riding'.
Anyhow, another part of the argument is that the US "won" in Ukraine already
The United States fought two wars to prevent a European hegemon from emerging in the 20th century. There is no potential European hegemon on or even over the horizon at the present. For all Russia’s bluster, it’s struggling to take even part of a much smaller, poorer neighbor—let alone hold it. It’s time to take the win.
... despite the small progress that Russia has been making on the ground and Putin's pronoucements that Ukraine would collapse in a week without Western aid. (Those claims implicitly get discounted.)
And the opposite of that, the claim that rather than it being a 'win', it's not clear how the US could win, or what a win would look like:
“We stand with Ukraine against Putin’s aggression. Everyone understands that he must be stopped. This is a very serious issue,” [Johnson] said. “But the White House is seeking billions in funding on that issue.”
“They haven’t given us any clear strategy, no appropriate oversight,” [Johnson] continued. “They’ve not explained to us what the endgame is.”
Finally, there's the 'but the Southern border comes first' argument.
“We understand the dire situation that we’re in. But the White House has to take care of our nation, and they’re not doing it,” [Johnson] said. “And that’s why our constituents are demanding answers, and that’s why we have to hold the line on this. We’ve got to force their hand to stem the flow at our southern border.”
And, of course, those who say that also reject the Senate compromise as not being hardcore enough on immigration.
A version of the latter is that the aid sent to Ukraine was more than enough to "build a wall" at the border with Mexico:
According to Breitbart, as the Trump administration spent $15 billion to cover 450 miles of the US-Mexico border with a wall of the nearly 2,000-mile border, it would roughly cost $60 billion to cover the entire border.
“Lo and behold, here is Ukraine being given, by the US, $US60 billion, which is apparently enough to build a wall across the entire US-Mexican border.”
This has been repeated in various ways in the past, e.g. in March 2022 (as IIRC the first package for Ukraine was being voted on):
Republicans just agreed to spend $14 Billion to defend Ukraine’s border. They refused $4 Billion to defend ours.
And actually made it into Senator Tuberville's speech recently--Feb 12, 2024:
We should not send a dime to Ukraine until our borders are fully secure. We have already given Ukraine more than $120 billion. This is more than enough money to secure every border in our country.
N.B. he also says that the money has been essentially wasted on killings that didn't lead to a diplomatic solution:
Unfortunately, but predictably, the $120 billion we’ve sent to Ukraine has resulted in a years-long stalemate that has cost hundreds of thousands of lives—both Ukrainian and Russian. [...] None of this has worked to either deter Russia or force parties to the table to negotiate a diplomatic solution. [...] Bring this war to an end. Stop the killing and bloodshed.
And there's the [final] jab that the US (administration) is trying to slow down Israel's war instead:
Joe Biden’s idea of diplomacy is sending Antony Blinken to Israel to tell Israel to slow down the war in Gaza. That’s not diplomacy. We need some REAL diplomacy in Ukraine.
And the slightly more elaborate version/list of America's priorities with Europe somewhere last:
There have been 160 attacks on our troops in the Middle East since October 7. We are also facing the possibility of war in the South China Sea, with China threatening Taiwan. A real leader has the right priorities. We cannot get involved in every conflict around the world.
[...] A land war in Europe is not America’s top priority. Even President Obama said, 13 years ago, we needed to “pivot to Asia” 13 years ago. [...] President Xi is watching America bankrupting ourselves for a war that gains us absolutely nothing.
Also, Tuberville says that that no aid should be sent to Gaza (either) because Hamas is stealing it. And right after he follows with (it's hard to conclude not intentionally juxtaposing) the claim that Ukraine has been wasting the aid through notorious corruption and "enormous theft".
Matt Gaetz said something similar:
I am against Joe Biden’s proposed $100 billion supplemental that combines aid for Ukraine and Israel together. It will create more challenges for our Southern Border and won’t make us safer abroad. Congress should not use the goodwill Americans have toward Israel to drag along our continued involvement in Ukraine.
Further, in the clip he describes Ukrane as a 'political weight' juxtposed to the 'close alliance with Israel' that needs to be 'well resourced'. Asked if he's worried about the outcome of the war in Europe, Gaetz says he's opposed to spending another $100 billion to find out 'which guy gets to run Crimea' and says he's worried about nuclear escalation [from Russia] and the well-being of US citizens if this 'tomfoolery' were to continue.
BTW, Trump recently suggested that the aid to Ukraine should take the form of loans. And he explicitly argued that all US aid should be like that, in fact:
Trump wrote in an all-caps post on his social media site Truth Social: “NO MONEY IN THE FORM OF FOREIGN AID SHOULD BE GIVEN TO ANY COUNTRY UNLESS IT IS DONE AS A LOAN, NOT JUST A GIVEAWAY. IT CAN BE LOANED ON EXTRAORDINARILY GOOD TERMS, LIKE NO INTEREST AND AN UNLIMITED LIFE, BUT A LOAN NEVERTHELESS.
He added: "THE DEAL SHOULD BE (CONTINGENT!) THAT THE U.S. IS HELPING YOU, AS A NATION, BUT IF THE COUNTRY WE ARE HELPING EVER TURNS AGAINST US, OR STRIKES IT RICH SOMETIME IN THE FUTURE, THE LOAN WILL BE PAID OFF AND THE MONEY RETURNED TO THE UNITED STATES.”
And he quickly found backing from Sen. Lindsey Graham on that idea. OTOH Romney called it a 'fig leaf', saying that Ukraine isn't going be able to repay.
And Trump also made the argument from priorities, saying about the war in Europe "it affects them much more. We have an ocean between us". And his general idea of how the US should transact in these matters: "You don’t pay your bills, you don’t get protection ... we are not going to be the stupid country of the world any longer." Video here of the latter speech. Trump also claimed there the US gave $200 billion to Ukraine, and Europe only $25.
And since the asker of this Q has already declared this answer to be "soapboxing", here's some of that to balance Trump's last claim somewhat:
FWTW, I also found this poll from September that found that "Non-Trump Republicans" found more value in the past aid to Ukraine, at least. The Q does seem separate the military from the civilian aid, and throws the defense budget figure in there for comparison, so it may be a bit leading. Anyhow, it's interesting that 70% of Trump supporters found the aid not worthwhile even from this perhaps most favorable prism, while the rest of Republicans were more split (53% : 46%).
Anyhow, if Orban is to be believed reporting on his conversation with Trump, this is part of Trump's plan for ending the war quickly.
Finally, while [thus far] I was not able to find Democratic Party congresspersons who oppose[d] Ukraine funding in itself, there certainly is extra-parliamentary "hard left" opposition, and their arguments are that the US is looking to transform Ukraine into 'Big Israel' etc.
