There is another aspect of this that shows Trump is not just creepy for looking, touching and speaking about his daughter "that way". He also said he'd date his daughter from his first wife when married to his second one. That's really fucking insensitive behavior to his wife. There is almost always tension between a step daughter and a man's second wife. It's a public humiliation of his wife. Just plain trashy behavior on Trump's part.
That said, this not what disqualifies Trump for prez. It's about as germane to the election as Bill's well known past regarding Lewinsky and other women when Hillary is the one running for office. It's a character issue that may or may not be important.
What disqualifies Trump among many other things are his incredibly dense ideas about national defense and the police action he promises to unleash on the people of this country to root out and deport 11 million people. Speaking of which, why is that a good thing to do?