How does that "tarnish" the GOP narrative?

True. Scott v Sandford held that Congress had no authority under the Constitution to limit slavery. And if Congress couldn't then the President certainly couldn't. Lincoln was no John Brown. No revolutionary.

But given the opportunity of civil insurrection, he first limited slavery, then abolished it via the 13th amendment. He approved Sherman's transfer of land & set up the Freedman's Bureau to provide education, fair work contracts, land titles, suffrage & prevent southern whites from effectively re-enslaving blacks.

Citing the chaotic circumstances with which the Bureau found itself, Du Bois writes: "Under these circumstances, the astonishing thing is that the Bureau was able to accomplish any definite & worth-white results; yet it did..."

It was Johnson, the Democrat, who undermined Field Order #15 & sabotaged the Bureau by vetoing Congressional appropriations.