He's simply a threat to their established hierarchy.
What part of "He is the established hierarchy" do you not get? Do you seriously think, for example, that a man who hasn't paid taxes in 18 years due to some bullshit tax code garbage is going to change that tax code, especially after his claims that it's just smart of him to do what he does? If what he does is smart, the opposite would be stupid. Do you think he is going to do something that he deems to be stupid, like pay his fair share of taxes? This whole "I'm the anti-establishment candidate you've been looking for all these years" shtick is absolutely ridiculous. I seriously can not believe that anybody buys it. It boggles the mind.
Do you not recognize the difference(s) of financial and political hierarchy?
How many rich or poor knowingly pay more taxes than the laws allow, even those rich that claim not to pay their "fair share"?
If President he would assume leadership of the party of which has displayed no particular fondness, throughout his brief political life as a Republican.
Unfortunately, in today's world you have to be high on both hierarchies to win. Could you imagine a poor person ever becoming The President now?
Poor is relative.
No such thing as a poor politician, just stupid ones.