The billionaire real estate developer said he wanted the Republicans establishment to treat him fairly, and he has seen that over the past few months.
"The best way for the Republicans to win is if I win the nomination and go directly against whoever (Democrats) happen to put up, and for that reason I have signed the pledge," he said, holding a copy of GOP's pledge with his signature on it.
Trump is the GOP front-runner—both nationally and in key primary states—according to every major recent poll.
Here is the text of the pledge:
I,_________, affirm that if I do not win the 2016 Republican nomination for President of the United States I will endorse the 2016 Republican presidential nominee regardless of who it is.
I further pledge that I will not seek to run as an independent or write-in candidate nor will I seek or accept the nomination for president of any other party.