Complex sentence: Kennedy's first major involvement in a national political campaign was his support in 1932 for Franklin D. Roosevelt's bid for the Presidency where he donated, loaned, and raised a substantial amount of money for the campaign.
Split into simpler sentences: Kennedy's first major involvement in a national political campaign was his support in 1932 for Franklin D. Roosevelt's bid for the Presidency. He donated, loaned, and raised a substantial amount of money for the campaign.