A surviving Lincoln or an alternative VP like Benjamin Butler with more proactive and dynamic leadership would make the Gilded Age less chaotic and more restrained, instead of having the robber barons running amok. Grant completely failed in handling the socio-economic changes brought about by rapid industrialization.
Or, let the CSA win but with a pyrrhic victory. The CSA would become a total joke that the North would quickly get over revanchism. Various progressive, liberal and leftist movements would unite and organize earlier due to a lack of racial struggle. Thus, we would see earlier and stronger organized labour and other progressive movements. American political development would resemble Canada.
In both cases, American politics would be dragged leftwards compared to OTL.