He only ran for President because of Obama, so it's no surprise. For some reason, (and it's not race) he has a unique level of disdain for Obama.
He hated him primarily because of his race. He may not say outright anything racist, but if you look at this actions and history I have every reason to believe he is a racist. Maybe not a KKK, Neo-Nazi type as lets remember racism is a spectrum and very few are actually 100% non-racist or 100% racist, most of us have some prejudices to some degree while few of us actually hate a race so much we want them wiped off the map. Rather if you look at Trump's past elections be it not renting to Blacks, quoting frequently alt-right sites, his various claims on Muslims, calling Mexicans racist, insulting an American born Indiana judge in the Trump University who has Hispanic, he definitely compared to pretty much every post WWII president most closely fits the mold of a racist.