The radical republicans differ from Lincoln's plan because they thought the war was easy towards the south.
Step-by-step explanation:
Radical republicans believed that the Lincoln plan for reconstruction was not harsh enough because from their point of view the south was guilty of starting the war and the deserved to be punished as such. The south needed to be rebuilt the civil war.
President Andrew Johnson, the successor to President Abraham Lincoln, after his assassination had a very difficult idea about it than with radical republicans.