The very term, “Radical Republicans,” sounds like an oxymoron, or it used to. That was before GW started on his blundering path down the road of reactionary leadership, and appointment of judges who seem to be living in the 19th century. Pretty radical to me.
Well, history makes strange turns indeed. After the Civil War (recall, Lincoln was a Republican) there was a big debate about how to treat the defeated South, i.e., the Confederacy, aka, the Rebels. Had they ever genuinely seceded from the Union, or, since that was not allowed, were they simply defeated rebels? Conquered belligerent nation or errant citizens entitled to due process? Thaddeus Stevens, the leader of the Republican Radicals, opted for the first description. A rock-solid egalitarian, he wanted equal rights for all, voting rights, established and protected for the freedmen (former slaves), and confiscation of the property of the southern elite to fund veteran’s benefits and land distribution to the blacks. He got some of it, but never all he wanted.
The north, and his party, were divided. Many did not like the notion of “negro rights.” Slavery was bad, but that was over, and it was time to move on. Some were eager to bring the rebels back into the fold of the Union, get their states’ delegations seated in Congress. Of course, many southerners, except for the minority of Unionists who were quaking in their boots in the midst of the general hostility around them, wanted to get back to normal as soon as possible so they could try to restore the status quo ante bellum. That is, slavery might be gone, but there was still plenty to do to keep the negroes down, what with lynching, racial cleansing of towns, debt peonage, and the like. Stevens understood all this and worked tirelessly for a Reconstruction program that would prevent it.
Eventually, in 1876, Reconstruction ended, and Jim Crow rushed in to fill the void in full force. The South stayed Democratic for generations, until Nixon managed to pry it loose on the basis of “values” politics. The Democratic Party evolved into the more liberal-progressive of the two major parties in the USA, but it always had to deal with its racist-segregationist element with deeply reactionary instincts that ruled the southern states.
As I say, the past is always present.