English: New York, 3 September 2015 (CNN). Donald Trump has signed the pledge.

The Republican presidential front-runner met privately with Republican National Committee Chairman Reince Priebus and signed a loyalty pledge. This means Trump has promised to support the party's eventual nominee -- whoever that may be -- and that he will not run as a third-party candidate.

Trump explained Thursday that he came to the decision to sign the pledge because the Republican Party in recent months has been "extremely fair" to him. RNC officials began circulating a pledge to various GOP presidential campaigns this week, measuring up how much appetite there is in the field to commit to supporting the eventual nominee.

"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," it reads. The pledge continues: "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."

The pledge has not only put pressure on Trump to commit to the party, it's also forcing some of his rivals to promise to support Trump if he were to clinch the GOP nomination. It's a particularly uncomfortable position for a candidate like Jeb Bush, who in recent weeks has publicly clashed with Trump. However, pressed on whether he would support Trump if he were to become the nominee, the former Florida governor answered in the affirmative.

"Yes, I would, of course. We need to be unified. We need to win," Bush said.

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