Answer:
They felt the plan did not go far enough to forgive former Confederate leaders
Explanation:
Radical Republicans thought Lincoln's southern reconstruction plan was too tolerant, with everything the Confederates did with the secession war. They felt that the reconstruction plan should be more rigorous, highlight the guilt that the southern states and their leaders had for encouraging the war and establishing a severe punishment for everything that the country was going through.
In other words, they thought the plan did not go far enough to forgive former Confederate leaders.