I think it would be congress
Zionism is the Jewish movement that can be described as the middle ground between the very conservative movement and the other more liberal branches.
After world war 1 the United States wanted to isolate themselves from things like that because of how bad the war was. They went as far as to not join the league of nations that their President made himself with other presidents. After the Korean War, they decided to not isolate themselves and meddle as much as possible to prevent the spread of communism because it would strengthen the Soviet Union who was the main enemy.
