How do I know?
First, because he's a bigot. He's an entrenched bigot against black, brown and yellow people. (Yeah: he asked that intelligence analyst where she was from and he wouldn't be satisfied with the answer "New York [City]" because all he could see was that she had Asian features.)
How do I know he's a bigot? Because in answering reporters asking about the "shithole" incident he called himself the "least racist person" we could meet. Nobody who's actually not racist ever makes such an asinine claim. Look up "overcompensation", Don.
The other reason I know he slandered Haiti and all of Africa? Because he denied it to reporters. For his entire political career he has proved himself a hardened, shameless liar. The examples are legion and everybody knows them. So when he denies saying horrible things, we assume he did say them because he lies the way fish swim — effortlessly.
Most politicians get the benefit of the doubt in their first couple of scandals. Trump exhausted that benefit before he was nominated.
Donald Trump, bigot and liar.
(Also an untrustworthy businessman whose corruptness we can only guess at but which we very likely cannot underestimate, and an ignoramus with zero intellectual curiosity. But I digress.)
That's how a solid majority of the nation views him. That's how history will remember him.
Because that's the ugly truth.