Donald Trump pledges Republican support, rules out third-party run

Donald Trump ruledout a possible third-party White House bid on Thursday and vowedto support the Republican Party's next presidential nominee even if it's not him.

To the dismay of Republican leaders,Trump has emerged as the overwhelming front-runner in the party's crowded field of leadership candidates, despite repeatedly insulting key constituencies and offering few details about his policies.

The billionaire businessman and reality television star has described Mexican immigrants as rapists, questioned Senator John McCain's war hero status and insulted a popular TV news host.

Trump is considered a longshot for the White House, but could undermine the eventual Republican nominee with an independent run for the presidency by splitting the conservative vote. Trump's declaration that he would not do so comes just weeks after he roiled the Republican race when, in response to the first question at the opening debate of the 2016 campaign, he refused to promise to back the party's nominee if he failed to win the leadership.

Trump was intensely lobbied by Republican National Committee leaders, who have struggled to rein him in, and announced his decision shortly after meeting privately with RNC chairReince Priebus.

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"The best way forward is if I win the nomination and go direct against whoever [the Democrats]happen to put up. So for that reason, I have signed the pledge," Trump said.

"So, I will be totally pledging my allegiance to the Republican Party and the conservative principles for which it stands, and we will go out and we will fight hard and we will win," he said.

Not legally binding

The decision puts an end for now to the nervousness felt inside the Republican party about the prospect of Trump holding firm and keeping his options open. At the debate, he said that gave him "a lot of leverage."

The pledge is not legally binding. Trump could always change his mind, particularly if Republican establishment leaders take aggressive steps to thwart his candidacy in the coming months.

If not for Trump, the need for such a loyalty oath probably would not exist. There had beenno doubts about the intentions of the Republicans' other major presidential contenders headed into the debate, and they quickly lined up Thursday to sign the pledge.

"The RNC clearly felt it had to box Trump into a decision," said Doug Watts, a spokesman for fellow candidate and retired surgeon Ben Carson. "We just sort of shrugged our shoulders, and that's the end of that."

The RNC's pledge asks candidates to promise to "endorse the 2016 Republican presidential nominee regardless of who it is." Further, it asks them to 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."

"It is, more than anything, your word," former technology executive and candidate Carly Fiorina said Thursday on CNN's New Day. "And I would presume that somebody running for president would like to signal to the American people, and most especially right now to Republican primary voters, that their word can be trusted."