After the 1920 election, newly elected Republican President Warren G. Harding appointed Hoover as Secretary of Commerce; Hoover continued to serve under President Calvin Coolidge after Harding died in 1923. Hoover was an unusually active and visible cabinet member, becoming known as "Secretary of Commerce and Under-Secretary of all other departments". He was influential in the development of air travel and radio. He led the federal response to the Great Mississippi Flood of 1927. Hoover won the Republican nomination in the 1928 presidential election, and decisively defeated the Democratic candidate, Al Smith. The stock market crashed shortly after Hoover took office, and the Great Depression became the central issue of his presidency. Hoover pursued a variety of policies in an attempt to lift the economy, but opposed directly involving the federal government in relief efforts.