My theory, Trump was meant to derail the republican party and assure victory for Hillary. They used to be very good friends after all, and they move in the same circles.

Trump has been talking about running for awhile, and even tried once before, so very influential people approach him and offer him some assistance. Trump takes it, and does what he always does, gives it 100% and takes no prisoners.

When he wins, the powers that be get him to go along with their plans, even if he wasn't the person they had groomed for the job, and when he goes off course, they get their establishment stooges to put on the brakes. RINOS allow Trump to act when it's beneficial to the elite, but stop him whenever he's doing genuinely good work.