But he's never suggested that he isn't a legitimate president, I don't think. And he also begrudgingly praised his recent speech in Poland.
But yes, his main problem with Trump is aesthetic. But bear in mind Harris is a man who is pathologically obsessed with ethical human behaviour, to the extent that he even wrote a book saying that lying is ALWAYS ethically wrong (except in cases where lying would keep someone out of danger). AND he's a vegan!
Basically, he's a proper weirdo. But I do love him.