On thrump this is why he wont make that pledge not to run on a third party ticket.

The Republican Party has the power to make sure he is not on the ballet on individual states in the primary.

He wants.to be on the ballot in every state. If he is an loses the primary he won't be on a third party ticket.

If they knock him off the ballet in some states. Then he can say he was not treated fairly by the republican part. Then he will run under a third party punishing the Republican Party.