WASHINGTON (CBSNewYork/AP) — Presidential candidate Donald Trump ruled out the prospect of a third-party White House bid Thursday and vowed to support the Republican Party’s nominee — whoever it may be.

The billionaire businessman announced his decision in a raucous news conference at Trump Tower, the gold-hued skyscraper in midtown Manhattan where he launched his surging and front-running campaign for president.

“I have signed the pledge,” Trump said, adding that he intends to win the nomination himself and face whoever the Democrats nominate.

“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,” Trump said.

Trump praised his treatment by the Republican National Committee.

PHOTOS: The Many Faces Of Donald Trump

“The RNC has been absolutely terrific over the last two-month period. And as you know that’s what I’ve wanted, I’ve wanted fairness,” Trump said. “I don’t have to be treated any differently than anybody else, I just wanted fairness from the Republican party.

The billionaire businessman and presidential candidate roiled the GOP race when he refused to make such a promise in the campaign’s first debate.

The front-runner was the only candidate onstage not to make the commitment to back whoever emerges from the party’s primaries.

“I am discussing it with everybody, but I’m talking about a lot of leverage,” Trump said to some boos at the debate. “We want to win, and we will win.”

A third-party bid by Trump, whose lead in what are still very early polls has held strong throughout the summer, could have harmed the GOP’s efforts to take back the White House after eight years of Democratic President Barack Obama.

The Republican National Committee extended the pledge to all the candidates seeking the party’s nomination to avoid such a scenario.

Trump met with RNC chief Reince Priebus on Thursday in Manhattan to discuss the pact.

If not for Trump, the need for such a loyalty oath probably would not exist. There were no doubts about the intentions of the GOP’s other major presidential contenders headed into the debate, and they quickly lined up Thursday to sign.

Among them: Ohio Gov. John Kasich, former Florida Gov. Jeb Bush and retired surgeon Ben Carson. Kentucky Sen. Rand Paul said he was likely to.

“Ross Perot ended up giving us the first Clinton, and I think if Trump does this (runs as a third-party candidate), he could give us another Clinton,” Paul said on “CBS This Morning,” referring to Democratic front-runner Hillary Rodham Clinton and her husband, former President Bill Clinton.

New Jersey Gov. Chris Christie signed the pledge during an appearance on Fox News on Thursday.

“I’ve made my decision. I want the nomination of our party, and I’ll support whoever the nominee is if it’s not me,” he said.

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 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.”

Trump’s decision about the pledge comes in the midst of an ongoing fight with Bush, who on Thursday on ABC’s “Good Morning America” charged that Trump was “trying to insult his way to the presidency and it’s not going to work.”

Bush said Trump’s policies are more in line with Clinton than Republicans. The day before, Trump told Breitbart News that Bush, who speaks fluent Spanish, should “set the example” by speaking English while in the U.S.

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

TRUMP’S MESSAGE: ATTACK ME AT YOUR OWN PERIL

Trump became almost gleeful when CBS2’s Marcia Kramer asked him what would happen to people who aired negative ads against him.

“One of the things I’m most honored about is that so far everyone who attacked me has gone down the tubes,” Trump said. “You have Lindsay Graham attacked me. He was at 3 percent. Now hes at zero. (Former Texas Gov. Rick) Perry attacked me. Now he’s getting out of the race. Rand Paul is down to less than 2 percent and he attacked me.”

Trump said that should be a cautionary tale for Bush, who just  launched a new campaign ad calling Trump a “germaphobe” and a “Democrat in disguise.”

“He’s going to spend lobbyist money and special interest money. Remember this: they have total control over Jeb and Hillary and anyone else who takes that money,” Trump said.

Trump had no shortage of opinions. He said the nuclear treaty with Iran is so bad Secretary of State John Kerry could, in his mind, replace Hillary Clinton as what he calls the worst secretary of  state in history.

Trump was also asked if he’d give his kids positions in a Trump administration. He said probably not.

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