That’s a hugely controversial question. Though American support for Israel really is massive, including billions of dollars in aid and reliable diplomatic backing, experts disagree sharply on why. Some possibilities include deep support for Israel among the American public, the influence of the pro-Israel lobby, and American ideological affinity with the Middle East’s most stable democracy.
The countries were not nearly so close in Israel’s first decades. President Eisenhower was particularly hostile to Israel during the 1956 Suez War, which Israel, the UK, and France fought against Egypt.
As the Cold War dragged on, the US came to view Israel as a key buffer against Soviet influence in the Middle East and supported it accordingly. The American-Israeli alliance didn’t really cement until around 1973, when American aid helped save Israel from a surprise Arab invasion.
Since the Cold War, the foundation of the still-strong (and arguably stronger) relationship between the countries has obviously shifted. Some suggest that a common interest in fighting jihadism ties America to Israel, while others point to American leaders’ ideological attachment to an embattled democracy. Perhaps the simplest explanation is that the American public has, for a long time, sympathized far more with Israel than with Palestine:
One very controversial theory, advanced by Professors John Mearsheimer and Stephen Walt, credits the relationship to the power of the pro-Israel lobby, particularly the American Israel Public Affairs Committee (AIPAC). Critics of this theory argue that AIPAC isn’t as strong as Walt and Mearsheimer think. AIPAC’s failure to torpedo the Iran nuclear deal during the Obama administration underscored the critics’ point.
Regardless of the reasons for the “special relationship,” American support for Israel really is quite extensive. The US has given Israel $118 billion in aid over the years (about $3 billion per year nowadays). Half of all American UN Security Council vetoes blocked resolutions critical of Israel.
Despite this fundamentally close relationship, there are occasionally tensions between Israeli and American officials. This was particularly true under US President Barack Obama and Israeli Prime Minister Benjamin Netanyahu; the two leaders clashed regularly over issues like settlements and Iran. The relationship reached a particularly nasty point when Netanyahu planned, with congressional Republicans, a March 2015 speech to a joint session of Congress that was highly critical of Obama’s approach to Iran. The Obama administration was furious over what it saw as Netanyahu conspiring with Obama’s domestic political opposition to undermine his policies.
The Trump administration has led to renewed warmth in the Israeli-American relationship, culminating in Trump’s December decision to formally recognize Jerusalem as Israel’s capital. The stark difference between Obama and Trump approaches to Netanyahu reflects a growing partisan gap inside the United States, with Republicans taking an increasingly hard-line “pro-Israel” position. If Democrats end up concomitantly becoming more willing to criticize the Israeli government, Israel may well end up a partisan issue in America — which actually would threaten the foundations of the US-Israel alliance.