On August 6, 2015, during the first Republican presidential debate, every candidate promised to endorse the eventual nominee.
Brett Baier asked the ten candidates:
Is there anyone on stage, and can I see hands, who is unwilling tonight to pledge your support to the eventual nominee of the Republican party and pledge not to run an independent campaign against that person.
Every candidate promised to endorse the eventual nominee – except Donald Trump.
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In September the Republican party asked the presidential nominees to sign a pledge to support the party and the eventual nominee.
Both Jeb! Bush and Lindsey Graham signed the pledge.