Complex sentence: In 1959, Symington, then chairman of the National Security Resources Board in Washington, D.C., was preparing to run in the 1960 presidential election and won the backing of former President Harry S. Truman, but eventually lost the nomination to Senator John F. Kennedy.
Split into simpler sentences: In 1959, Symington, then chairman of the National Security Resources Board in Washington, D.C., was preparing to run in the next presidential elections. Later, Symington ran in the 1960 presidential election and won the backing of former President Harry S. Truman, but eventually lost the nomination to Senator John F. Kennedy.