In 1937, Chaim Weizmann gave testimony before a British Commission of Inquiry regarding British policy and reported on it to that year's Zionist Congress.
One of the things he had to say was very disturbing, especially in the light of what eventually happened to the Jews of Europe. He was asked "But can you bring 6,000,000 to Palestine?" and he replied: "No" as he was well acquainted with the laws of physics and chemistry.
Weizmann spoke of 6,000,000 Jews of whom he was determined to save the 2,000,000 youngsters who were fit for Eretz-Yisrael. The others, the old people, were as "dust", who would disappear. "Two millions, and perhaps, less - Scheerith Hapleta - only a branch shall survive. They had to accept it.
Here's the text as it appeared in the official monthly of the World Zionist Organization (see the underlined section in the right-hand column):-
The clipping is from The New Judea, August-September 1937, page 215.