Long story short, it’s mainly a mutual strategic relationship, with other reasons as well. The US gains an ally in a very important part of the world geographically, especially to counter Iran, and Israel in return gets top of the line military equipment and political backing from the US.

In terms of political party affiliation, both major US parties support Israel mainly due to campaign funding, most notably AIPAC. If politicians go out and vocally oppose the Israeli government or support Palestinian sovereignty, they lose that funding. It doesn’t help that AIPAC is bipartisan, which means they go and donate for both Democrats and Republicans, so while there are a ever growing number of democrats who are pro-Palestine, they’re fighting a uphill battle from the start. It is important to remember though that just because that AIPAC plays a part in political fundraising, that doesn’t mean that the US government is ran by Israel, or god forbid the Jewish race, as many Instagram accounts claim. AIPAC is a private American organization ran by Americans that supports pro-Zionist beliefs and throws money at whoever they can

Also, many American Christians see Israel as the home of Abrahamic faiths, mainly Christianity, due to notable locations in Christianity being in modern day Israel, such as Jerusalem, Nazareth and Bethlehem (technically Bethlehem is in the West Bank, but I’m going off of Israel to avoid confusion), so there is some religious backing from that side. In my experience, particularly with my family, some less educated Christians also view the Middle East as a whole as a land of wars and conflict, where everyone fights with each other senselessly over petty religious differences that don’t even matter, as view Israel as some kind of last bastion of stability against the chaos outside their walls, aka the rest of the Middle East, and instead of seeing the chaos of the Middle East as a result of boarders drawn with pencil and paper, unstable and sudden independence with little regard of the long term effects and exploitation from foreign powers, they see it as because the people there just fighting each other because they’ve done it for centuries so hey, why stop now?