If Kanye tweets about some obscure artist, that person isn't all of sudden mainstream. That person becomes mainstream only when she is widely played.

That's why folks are saying he's not mainstreaming the alt-right. He is way late to the party. It's been mainstream. The fact that alt-right is common terminology illustrates that.

He brought this particular lady's name to the attention of some new people. But him just mentioning a name doesn't make the ideology or movement normalized.

It is mainstreamed when it is talked about widely and openly. It isn't taboo to talk about alt-right ideas anymore. It's been mainstream for a couple of years.