This is heavily dependent on cultural context
Being Canadian and therefore living close to the USA, is in this case the context.
During the early 19xx years, racism was very normal, and one of the ways this was expressed was with Blackface, which was often used similar to how clown makeup is used to day. It wasn't flattering. Therefore, his activities remind everyone of that racist time. I don't believe he's actually racist, but the association is still there and politically.. unfortunate for him.
Why is this a big deal now and not 20 years ago?
Basically, because there's a lot more communication due to social media and the internet. For centuries, until some 5-ish years ago, where I live, the Netherlands, we had something which is physically the same as blackface (Zwarte Piet), but it had grown from a totally different orgin - it didn't refer to skin color, instead being based on how they'd look like after crawling to a chimney - in an age where the primary means of heating in your home was with a fire in a hearth. Chimney sweepers just became black from the soot.
However, now people are considering it racist, because they're applying USA cultural standards to our own historical culture. So the context is changing, and in the USA cultural context, it indeed looks racist.
I'm making this example mostly because you seem to come from another culture where racism isn't prevalent.