Complex sentence: Warren was also the nominee for Vice President of the Republican Party in 1948, and he chaired the Warren Commission, which was formed to investigate the 1963 assassination of President John F. Kennedy.
Split into simpler sentences: Warren was also the nominee for Vice President of the Republican Party in 1948. He was appointed to chair what became known as the Warren Commission, which was formed to investigate the 1963 assassination of President John F. Kennedy.