Underrated by Northerners, Overrated by Southerners.
His writings on slavery don't seem any more racist than Abraham Lincoln's, and his racial problems were societal problems.
True. Most people forget, if they ever knew it, that abolitionists were but a fringe part of the Republican coalition. For most Republicans, they just wanted to ensure that white workingmen didn't have to compete with blacks, be they slave or free, either in the north or in the western territories. Keeping down competition for jobs and land was also a factor in the nativist Know-Nothing Party becoming part of the Republican coalition as well.
Republican Party nativists were especially aggrieved at the demographic changes of the country. For many of these WASP nativists, the Irish catholic wave was bad enough, but seeing the south importing more and more Africans? They were really upset about what slavery could mean for their precious white future of the country.