In all seriousness, this is an example of Trump's negotiating skills. Trump gave up nothing (a third party bid would be an impossibility given that most filing deadlines are the same dates as the primaries so he couldn't run without dropping out now) and what does he get in return for dropping the empty threat of an impossible third party run? A vow that if he wins the nomination the 16 other candidates will pledge support, something that is both useful and gratifying to Trump (Lindsey Graham's endorsement will be wonderful). A good deal.
But endorsement/support actually means nothing. The RNC isn't forcing candidates to actively campaign for the winner. For all we know, if Trump gets the nomination, Bush or Graham can appear on TV and say "yes, I support Trump, he has my endorsement" and then disappear for the rest of the campaign. As long as they don't actively campaign against him of course.
