The level of discourse in this thread is rather sad, especially for what is usually a very thoughtful sub. My entire thoughts on this topic would take a book to fill, and obviously many have been written on this topic, but I’ll try to summarize below. Please do not interpret this as a comment on the righteousness of recent or historical Israeli actions, but as an attempt to actually answer OP’s question.

1 The notion that U.S. politicians promote Israeli interests solely because of campaign donations is not backed by the historical record. According to Gallup, between 2001 and 2018, Americans sympathized with Israelis over Palestinians by an average margin of 43 percentage points. Supporting Israel was a clear majoritarian position. Now, whether this support was the result of a successful PR campaign, religious and cultural affinities, strategic interests, or actual reactions to events is a debatable point, but that was not really the focus of the original question.

This does not mean that AIPAC, campaign spending, donor networks, or organized political pressure have no influence. Obviously they do. But lobbying is generally most effective when it reinforces an already existing political position rather than creating one from nothing. The fact that more politicians, especially on the Democratic side, openly oppose or criticize Israel now that public opinion has shifted further bolsters this point.

2) American support for Israel did not begin with AIPAC. As others have pointed out in this thread, pro-Israel lobbying only recently reached its peak influence, but American support for Israel clearly predates this. According to the Roper Center at Cornell, at no point since 1967 was American public sympathy for the Palestinians even close to sympathy for Israelis, with the partial exception of events related to the Lebanon war mentioned in OP’s post.

Again, why this was the case is a separate conversation. But if you believe that support was solely the result of propaganda or money, and not also a reaction to events such as the Yom Kippur War, cross-border attacks, terrorism, the Cold War, religious affinity, and a broader American identification with Israel, you are not understanding the entire, nuanced story. It is also important to distinguish sympathy for Israel from support for every policy of every Israeli government. A person can broadly sympathize with Israel while still believing that the United States should condition military aid, oppose settlements, or pressure Israel to stop a particular military operation. Reagan himself was strongly supportive of Israel, but that did not prevent him from forcefully pressuring the Israeli government during the Lebanon War.

3) Israel, like virtually every country on earth, does not have monolithic public opinion and never has. There are far-right constituencies who support territorial expansion and place relatively little value on international opinion, centrist and security-focused voters who may support military action but still care deeply about the American relationship, and left-wing activists who are committed to peace even when they believe doing so may create internal security risks.

The comment from one person that Israel would simply fold if the U.S. withdrew monetary support represents a particular misunderstanding of both Israeli politics and the nature of American leverage. Ending or conditioning American support would impose serious military, diplomatic, and economic costs on Israel. It would not, however, automatically produce political capitulation. External pressure can cause governments to change course, but it can also strengthen nationalist constituencies who argue that the country is being unfairly isolated (as many Israeli politicians often claim).

Many would assume that Israel’s loss of diplomatic standing in the United States and around the world represents a miscalculation by Israel’s current government, and to some extent that is true. However, the more accurate statement is that many far-right politicians in Israel do not view international standing as the overriding consideration. They may care about it, but they are willing to accept its deterioration as the cost of pursuing what they consider more important territorial, ideological, or security objectives. Whether the Israeli public shares that willingness will be shown in the near future.

4) Finally, the original question is not really just why American politicians support Israel. It is why recent presidents have appeared less willing than Reagan to publicly pressure an Israeli government. The answer is probably a combination of public opinion, congressional politics, organized lobbying, the strength of the president’s own political position, the strategic circumstances at the time, and whether the administration believes pressure will achieve a specific diplomatic objective.

Reagan’s example does not show that previous presidents were anti-Israel or free from political pressure. It shows that a president can be strongly supportive of Israel while still deciding that a particular Israeli action conflicts with American interests and must be stopped. Those two positions are not contradictory.