Because when provided with positive evidence of obvious bias, you demanded proof of a negative which is ranges from prohibitively difficult to impossible. This is not a valid form of reasoning. The inability to disprove something is not a valid reason to believe in it.
Let me put it another way, I don’t converse with paedophiles so I’m going to need proof that you’ve never diddled kids before we can continue.
This is absolutely true because Trump is fundamentally not a fluke, but rather the inevitable culmination of festering rot at the core of American culture. If not him, it would have been someone.