on May 14, 1948, the United States, under Truman, became the first country to extend any form of recognition. This happened within hours of the Jewish People's Council gathering at the Tel Aviv Museum and David Ben-Gurion declaring "the establishment of a Jewish state in Eretz Israel, to be known as the State of Israel".

Following UN mediation by American Ralph Bunche, the 1949 Armistice Agreements ended the 1948 Arab Israeli War. Related to enforcement of the armistice, the United States signed the Tripartite Declaration of 1950 with Britain and France. In it, they pledged to take action within and outside the United Nations to prevent violations of the frontiers or armistice lines;

The US basically guaranteed Israel from the beginning, but in terms of the modern "all in for Israel" policy, that wasn't until the early 1960s, so you can change my decades to 60 instead of 70 years if you count it from then. In the 50s Germany and France were giving Israel a lot of stuff, so the US wasn't as necessary.

But yeah in the 50s the US was stupidly hell bent on de-colonialism and that led the the idiotic decision to side with the USSR and Egypt in the Suez Crisis.