In 1938, Cahill married Dorothy Canning Miller, curator of painting and sculpture at the Museum of Modern Art. The following year, he took a leave of absence from the WPA to stay in New York City and direct a large survey exhibition at the 1939 World’s Fair, "American Art Today". Through Miller, he continued to meet new artists and he was an avid and interested spectator of all of the programming at the Museum of Modern Art.