The event that raised concerns among the Radical Republicans about the future of the nation and the process of Reconstruction following Abraham Lincoln's assassination was Andrew Johnson's presidency.
Johnson, who became president after Lincoln's death, had a more lenient approach to Reconstruction than the Radical Republicans desired. His policies and actions, including his efforts to quickly restore the Southern states to the Union without ensuring protections for the newly freed slaves, led to significant tensions and conflicts with the Radical Republicans in Congress, who sought to implement more stringent measures and protect the rights of African Americans.