Eleanore Roosevelt, imaginable if FDR had nominated Henry Wallace as VP and Wallace were headed to defeat.
Early in 1948, there actually was discussion about nominating Eleanor Roosevelt for Vice President. There was a decent amount of press speculation, and there were some Democratic insiders pushing for it. The ND Democratic Party even called for a "Truman-Roosevelt" ticket.
No offer was made and Eleanor put the kibosh on the proposal. NY Dems also tried to recruit her to run for Governor of NY and for Senator, which she also turned down.
