Yes, Zionism was powerful in the US even before Israel self-declared itself a state, and continues to this day. This oral interview with Edwin M. Wright talks about Zionist/Jewish influence in the White House. It's from the Truman Library:
Edwin M. Wright
General staff G-2 Middle East specialist, Washington, 1945-46; Bureau Near East-South Asian-African Affairs Department of State, since 1946, country specialist 1946-47, advisor U.N. affairs, 1947-50, advisor on intelligence 1950-55.
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