I mean I agree he probably is, but that is a scary level of certainty you have there.
True racism is inherently hard to pin down unless the person actually states something like "I belive black people are en inferior species". Doing something racist or saying something racist doesn't necessarily make you a racist, they aren't necessarily racially-hate motivated acts of words. This is especially hard when dealing with a colossal idiot like Trump, it's not like the amount of dumb shit he says and does is limited to the racial realm.
That said, yeah I wouldn't blame anyone for thinking he's a racist. I think him being a dumbass probably should take center stage, bit he does certainly do and say a lot of racist shit.
Leaving that aside... you have a person's own words and actions, what more could you possibly require to draw a reasonable conclusion which is also one that is widely accepted among not only those who are trusted in their assessments of current events and politics but also those who personally know the person. It's never even been debatable.