It's no secret. He threw northern journalist in prison for extended periods of time and tried charging them with treason and no due process because they were unfavorably reporting on the war and his actions. There are court cases and plenty of documentation about all of this.

The trade restrictions and embargoes he placed on southern businesses which caused the civil war were also unconstitutional (although that would depend on your interpretation of the constitution).

And as for him being a racist here are some juicy quotes for you.

"Our republican system was meant for a homogeneous people. As long as blacks continue to live with the whites they constitute a threat to the national life. Family life may also collapse and the increase of mixed breed bastards may some day challenge the supremacy of the white man." -Abraham Lincoln

“I will say then that I am not, nor ever have been in favor of bringing about in anyway 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 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. I say upon this occasion I do not perceive that because the white man is to have the superior position the negro should be denied everything.” -Abraham Lincoln

I am not making anything up...