I'm glad you asked!
-He makes up statistics that portray African-Americans in a negative light
-He was investigated (and sued) by the Department of Justice because he refused to rent properties to black people
-He was fined by the state of New Jersey because he forcibly removed all the African-American casino dealers from the floor when certain people came to play
-He claimed that laziness is a trait in blacks
-He also said the only people he wanted counting his money were short guys in yarmulkes, claiming that he hated black people counting his money
-He has been a head charger of the birthing movement against President Obama
-He claims that Mexican immigrants are rapists and thugs
-He called a black person "his African-American"
-During a meeting with a house subcommittee, he questioned the heritage of Native American people by saying "They don't look like Indians to me!"
-He encouraged mob justice that led to the wrongful and racially motivated conviction of the Central Park Five
-He called his supporters "passionate" when they beat the everliving piss out of a homeless Latino man
-And, though not explicitly said by Donald Trump, KKK leader and white supremacist David Duke said "A lot of the things that he (Trump) believes are the same things we believe"
Of course if you believed up until this point that Trump wasn't a racist, there's no way you're going to be moved by any evidence. So, if you want to sit back and shout "cuck" that's fine, and if you want to sit back and shout about how Mexicans and Muslims aren't races that's fine. But just know that you're wrong, and you should feel bad about your wrongness.