I think he would be shocked. Compared to the norm today, Abraham Lincoln would be considered racist - even if he was radically liberal during his time period. There are quotes where he hints that the African American population would never intermingle. A half white half black president would have been a culture shock!
"I will say, then, that I am not, nor ever have been, in favor of bringing about in any way the social and political equality of the white and black races--that I am not nor ever have been in favor of making voters or jurors of negroes, nor of qualifying them to hold office, nor to intermarry with white people; and I will say in addition to this that there is a physical difference between the white and black races which will ever forbid the two races living together in terms of social and political equality. And inasmuch as they cannot so live, while they do remain together, there must be the position of superior and inferior. I am as much as any other man in favor of having the superior position assigned to the white race.
...notwithstanding all this, there is no reason in the world why the negro is not entitled to all the rights enumerated in the Declaration of Independence--the right of life, liberty and the pursuit of happiness. I hold that he is as much entitled to these as the white man. I agree with Judge Douglas that he is not my equal in many respects, certainly not in color--perhaps not in intellectual and moral endowments; but in the right to eat bread without leave of anybody else which his own hand earns [the Republican version of what the other rights amount to?], he is my equal and the equal of Judge Douglas and the equal of every other man.
(v. 3, pp. 247-8. Sixth Debate with Steven A. Douglas at Quincy, Ill., Oct. 13, 1858)"
He may have been pandering to the norms of that time period - but I doubt it. None the less, he was very liberal and obviously liberating.