There are plenty of things I don't like about the modern republican party. That they are not violent enough is not one of them. (This is not to say it is bad to shoot enslavers)
Lincoln in 1858, from the Lincoln-Douglas Debates:
"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, [applause]-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 I believe will forever forbid the two races living together on 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, and I as much as any other man am in favor of having the superior position assigned to the white race."
Now, imagine the people who would go to war with somebody who stated that publicly.
Lincoln was no saint, but among the universe of mid nineteenth century American elites, he was about as good as could be expected to win an election, and hell, in 1858 he didn't manage to unseat Douglas because he was considered too progressive on the issue. From that same L-D debate, Number Four:
I say, then, there is no way of putting an end to the slavery agitation amongst us but to put it back upon the basis where our fathers placed it, [applause] no way but to keep it out of our new Territories [renewed applause]-to restrict it forever to the old States where it now exists. [Tremendous and prolonged cheering; cries of "That's the doctrine," "Good," "Good," &c.] Then the public mind will rest in the belief that it is in the course of ultimate extinction. That is one way of putting an end to the slavery agitation. [Applause.]
Yes, he was a white supremacist that opposed slavery and his opponent was a white supremacist that supported slavery. He was still a white supremacist.