The reason why support for Ukraine is so shaky is that Republicans have been thoroughly compromised by the nation that started the war and has an interest in removing American support for Ukraine. Trump is far from the only leading Republican who is bought and paid for by Moscow.
Israel is an entirely different matter. As much as Netanyahu is a terrible person, he did not start this war and had absolutely no other choice than to respond to Hamas murderous rampage with a campaign to remove the terrorist organization. There was no other option and someone far further left on the political spectrum would have to do the same. Hell, any nation on Earth, including the most peace-loving ones, would have started a full-on war in reaction to attack like this.
The relationship between Israel and the USA is also far firmer than between Ukraine and the USA and not just because of the routinely overstated influence of the "Israel lobby". Israel is a far more important country, the most important Western partner in the Middle East for strategic reasons alone. It's a hub for cutting-edge research in pretty much all areas, from biotech to defense and it houses some of the most important chip fabs in the world - think of it as a second Taiwan. It's also a startup hub, one of the most important places for new high-tech companies to emerge in the world. You have very likely used technology and inventions that came from Israel without knowing it. Intel for example has had a presence in the country since the 1970s, pretty much since the beginning of close US-Israeli ties, and benefited massively from the research and development that happened there.
Israel is small and surrounded by enemies that have tried to destroy it and its people (what do you think "From the river to the sea!" actually means?) from the moment it was conceived by the UN. You are making a serious and sadly these days very common mistake of falling for a massive worldwide propaganda campaign - fueled by Iran, Russia and China, who are doing it in an attempt to weaken one of America's most important strategic partners - that tries to portray the justified, if brutal, war against an organization that does everything in their power to get as many civilians on both sides killed as a genocide, while at the same time ignoring the real and openly stated genocidal intentions of this terrorist pseudo-state and its supporters. The whole genocide argument falls apart at even the most cursory glance: Why would a country with genocidal intentions go through enormous lengths to minimize civilian casualties, far more so than any other country in the world? The IDF is the only military on the planet that is routinely informing civilians through calls, messages, flyers, hacked TV stations, web services, etc. before air strikes and ground operations. This is nearly completely unheard of elsewhere and entirely unheard of at this kind of scale. This actually hurts Israel militarily, as it allows not just civilians, but also terrorists to get away.
Why would they go through all of this trouble if the aim was to exterminate a people? How would a pluralistic democracy where Israeli Arabs (they don't like to call themselves Palestinians) have representation in the Knesset and even a Supreme Court judge decide to commit genocide anyway? Not to mention, if they were truly genocidal, they would start with the members of this people within their own borders, with an increasingly harsh campaign to separate them from the majority to slowly lead over to extermination, which is the opposite of what's happening in Israel, where - despite some very real discrimination, not too dissimilar to minorities in other developed nations - Israeli Arabs has gained more rights, influence and representation instead of less over time.
Note that I'm not saying that there are no war crimes being committed by Israel in Gaza. That would be preposterous. I'm certain that, just like in sadly any war, there are individual soldiers satisfying their blood lust. I'm also not denying that Palestinians have experienced and are experiencing countless injustices from the Israeli state and individual Israelis, especially settlers. This is however entirely different from the allegation that there is a planned, systematic campaign to murder an entire people. I think many people who are parroting this claim have good intentions, but are simply too inexperienced with what wars look like, mistake the absurd overrepresentation of this conflict in the media compared to other, much worse ongoing wars with this war being much worse. Assad had - in a single prison - about as many people murdered as have allegedly (we only have Hamas numbers) been killed in Gaza. The civil war in Sudan has seen massacres at a near incomprehensible scale, with tens of thousands dying over the course of days - yet barely anyone is talking about this. Why is that? Why are we all so obsessed with this tiny strip of arid land in the Middle East? I'm not saying that we shouldn't be watchful, that the international community should not be Israel's bad conscience, but there is still something profoundly wrong with the way our media - both news and social media - elevates this conflict above every other war.
Sorry for the wall of text. I hope you don't mind it and the fact that I have some opinions that go against the majority in this community.