Please answer a question about the following article about Dwight D. Eisenhower:

Eisenhower's stint as the president of Columbia University was punctuated by his activity within the Council on Foreign Relations, a study group he led as president concerning the political and military implications of the Marshall Plan, and The American Assembly, Eisenhower's "vision of a great cultural center where business, professional and governmental leaders could meet from time to time to discuss and reach conclusions concerning problems of a social and political nature". His biographer Blanche Wiesen Cook suggested that this period served as "the political education of General Eisenhower", since he had to prioritize wide-ranging educational, administrative, and financial demands for the university. Through his involvement in the Council on Foreign Relations, he also gained exposure to economic analysis, which would become the bedrock of his understanding in economic policy. "Whatever General Eisenhower knows about economics, he has learned at the study group meetings," one Aid to Europe member claimed.

While Eisenhower was president of Columbia, what group did he also work with?
Council on Foreign Relations