Answer:
Radical Republicans expanded their Congressional majority in the elections of 1866.
Step-by-step explanation:
President Johnson had a different view of the Reconstruction, he defended that the southern states did not give up their right to govern themselves and the federal government had no right to determine a series of questions that were state-level questions.
Because of that Johnson gave the southern states the free reign to rebuild themselves. This caused the creation of the black codes, that were a series of laws that removed the basic rights of African Americans.
This ideas of President Johnson caused him to lose northern votes in the congressional elections of 1866. Congress then passed the Reconstruction Act of 1867 that divided the South into 5 military districts and outlines how governments should be organized.