Presidential candidate Donald Trump has ruled out the prospect of a third-party White House bid and vowed to support the Republican Party's next presidential nominee - whoever it may be.
The billionaire businessman announced his decision in a raucous new conference at Trump Tower, the gold-hued skyscraper in midtown Manhattan where he launched his surging and front-running campaign for president.
"The best way forward ... to win, 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," Mr 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.
Trump's decision comes weeks after he enlivened the race for the Republican nomination 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 fell short.
He was intensely lobbied by Republican National Committee leaders, who have struggled to rein in the unpredictable former reality television star. Mr Trump announced his decision shortly after meeting privately with RNC chairman Reince Priebus.
The decision puts an end - for now - to the nervousness felt inside the Republican party about the prospect of Mr 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. He could always change his mind, particularly if Republican establishment leaders take aggressive steps to thwart his candidacy in the coming months.
"I see no circumstances under which I would tear up that pledge," Mr Trump said.
If not for Mr Trump, the need for such a loyalty oath probably would not exist. There were no doubts about the intentions of the Republicans' other major presidential contenders headed into the debate, and they quickly lined upto sign.
"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."
A third-party bid by Mr Trump could harm the Republicans' efforts to take back the White House after eight years of Democratic president Barack Obama. He leads the Republican field in what are still very early polls.
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."