Eager to increase its influence in the region, and prevent Nasser from going over to the Soviet Bloc, U.S. policy was not to become too closely allied with Israel. In the early 1960s, the U.S. would begin to sell advanced weapons to Israel (Hawk anti aircraft missiles), but also to Egypt and Jordan.
During Lyndon B. Johnson's presidency, U.S. policy shifted to a whole-hearted, but not unquestioning, support for Israel. Prior to the Six-Day War of 1967, U.S. administrations had taken some care to avoid giving the appearance of any active military alliance.
Leading up to the war, while the Administration was sympathetic to Israel's need to defend itself against foreign attack, the U.S. worried that Israel's response would be disproportionate and potentially destabilizing. Israel's raid into Jordan after the Samu Incident was also troubling to the U.S. because Jordan was also an ally, having received over $500 million in aid.
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Much to its pleasure, especially for the time, the United States saw a democracy defeat the combined forces of multiple Soviet-backed countries. Following the war, the perception in Washington was that many Arab states (notably Egypt) had permanently drifted toward the Soviets. In 1968, with strong support from Congress, Johnson approved the sale of Phantom fighters to Israel, establishing the precedent for U.S. support for Israel's qualitative military edge over its neighbors. The U.S., however, would continue to supply arms to Israel's neighbors, Lebanon and Saudi Arabia, to counter Soviet arms sales in the region.