Leonard Allen spent a significant portion of his career in Congress, where he chaired the Committee on the Census and was a delegate to the Democratic National Convention. He demonstrated steadfast leadership within the Long organization and consistently advocated for specific immigration policies, opposing the repeal of the Chinese Exclusion Act and introducing the Renunciation Act of 1944. Allen's career trajectory included a transition from high-level congressional roles to other pursuits, as evidenced by his decision not to seek re-election in 1952.

Leonard Allen's political identity is marked by a staunch opposition to immigration reforms, particularly in his resistance to repealing the Chinese Exclusion Act and his introduction of the Renunciation Act of 1944. Despite his alignment with the Long organization, his legislative actions reveal an unexpected rigidity on immigration issues, suggesting a highly localized or regionalist approach to national policy. Allen's consistent stance on these matters highlights a conceptual tension between progressive organizational ties and conservative immigration policies.