Since when does a political party have the right to dictate who is on an election ballot? Priebus can't limit Donald Trump from placing his name on any ballot. He can pledge to follow whatever rules apply to debates, but, there is no law stating a party can limit a candidate from the ballot. That is ridiculous. He can pledge all he wants, but, who is to say without his ability to run independently the RNC will continue to treat him fairly? In his early days there is every indication that wasn't going to happen.

It is no different than the tax pledge, it is about votes and the extreme conservative demands on a candidate. There is no law stating they have to maintain any pledge.  

July 10, 2015
By Paul Singer

It is a quirk of American democracy: (click here) Your choices for president depend on which state you live in.

For instance, voters in Colorado and New Mexico who do not want to vote for Mitt Romney or Barack Obama for president will have the option to vote for Virgil Goode of the Constitution Party, Libertarian Gary Johnson or several others — but those candidates will not be on the ballot in neighboring Oklahoma.

While Republicans and Democrats are campaigning already, third parties are scrambling this summer to master the intricacies of ballot-access laws in each state just to get their presidential candidates on the ballot.

"The time, money and energy spent getting on the ballot is more than the time, money and energy spent once we are on the ballot in most of these states," said Phil Huckelberry, co-chairman of the Green Party's ballot access committee....

I'd be worried he would run as an independent in 2020 if he is dissatisfied with the outcome in 2016. Donald Trump needs to run on his own terms this primary season. It is the only way to establish his ability to carry a constituency. The ballot for 2016 is not set and there is nothing saying he would drop out of the debates only to run as an independent. Priebus is causing a problem far greater than if he was allowed to run without special pledges. I hope the rest of the candidates are being asked to sign a certain pledge to the RNC. 

The RNC needs to make this a part of their platform so this pledge is a part of their requirements for debates from now forward. If it is not included in a platform, this election is rigged.

The upside of such a pledge to the RNC is that when Trump is the nominee no one else in the current field can run against him.