In 1865, the political situation was extremely fluid. By 1869, the Democrats had established themselves as leaders of the white South in opposition to Yankee occupation. There were some Republicans, but nearly all of these were wartime Unionists propped up by the occupying army. They were labeled "scalawags" and regarded as traitors.Would the *immediateness* of this under Lincoln post-war make *all* that much difference than it being delayed until the onset of military/Congressional Reconstruction led governments, and then the Grant Administration and then their appointments of men aligned to the Republican Party to offices? Why so?
The lines had been drawn, and it was going to be almost impossible for Republicans to muster any white support in the Deep South.
IMO, in 1865, there were many former Whigs who might have been recruited to the Republican cause, which embodied many traditional Whig ideas. But they would have to be approached right away.