He served in the United States Navy as a deck officer during World War II.
After the war, Smith attended the University of Chicago, where he received his master's degree in 1947 and his doctorate in 1949.
He wrote well-received biographies of Missouri Senator Thomas Hart Benton, presidents James Buchanan, Zachary Taylor, and Millard Fillmore, and Maryland politico Francis Preston Blair.
[2] Smith ran unsuccessfully as the Democratic challenger to Republican incumbent United States Senator Bourke B. Hickenlooper of Iowa in 1962.
Smith served as Lyndon B. Johnson's Iowa campaign manager in 1964, and ran again for Senate as the Democratic challenger to Jack Miller in 1966.